It's 9 p.m. on Christmas Eve and you need a doctor. You consider:

Going to the emergency room.

Or:

Driving down the street to one of those urgent-care clinics that keep popping up near busy intersections. Only problem is, you have no idea of what goes on inside. Maybe they just pass out Band-Aids. Then again, perhaps they're ERs in disguise?

Afraid not, says Dr. Kerry Johnson, who was an ER doctor until he partnered with Dr. Gary Gerlacher to open Acute Kids Urgent Care in 2003. While his office can't do everything an ER can, they've tried to fill a niche, he says.

"We were all pediatric emergency medicine docs who were kind of frustrated that the system was so slow," he says. "The kids would come in and wait four hours to be seen, so we said, 'You know what? There's got to be a better way.' We've tried to put the service back into health care."

How? Dr. Johnson utters a shocking statement: "The average time is less than 30 minutes, from checking in to going home."

At the 19 CareNow clinics in the Dallas-Fort Worth area, which serve adults as well as children, you can figuratively get in line by logging on from home, says Julie King, the front-desk coordinator at the Grapevine clinic.

"We just want the patients happy," she says. "Unfortunately, with the flu season coming upon us, it's inevitable that the waits will be longer and longer, but we offer pagers so the nurse can call you when the room is ready." And for those who'd rather try their chances elsewhere, "We can also call another clinic to get an accurate wait time."

It's not that anyone wants to replace emergency rooms. "There are things that are absolutely more appropriate to be handled there," says Acute Kids' Dr. Johnson.

The key is in knowing how to tell the difference.

Dr. Johnson, Ms. King and Dr. Mark Till, chairman of emergency medicine for Presbyterian Hospital of Dallas, weigh in with advice.

Here are a few surprising answers to common scenarios that can often occur at inopportune times:

During the office holiday party, your tooth begins throbbing so badly you begin yelping and moaning like a wild animal. (The boss is not amused.) "If it's Friday night and you're in agony, most dentists would probably meet you on Saturday" at his or her office, says Dr. Till. Then again, if you notice a large abscess that has spread to the jaw, "it's a bigger deal. Once it gets past the tooth, you need to go to the ER."

At the same office party, someone pokes you in the eye with a pen. (Wild party!) "If you do something to your eye, yes, you should come to the hospital," Dr. Till says, listing possible ailments such as corneal abrasion, an infection or a "perforated globe." For those reasons and others, "you need an emergency room."

You awake with a tummy ache. "The gamut for what belly pain can be is huge," says Dr. Till. It could be that chicken chimichanga you inhaled in one bite, or your appendix might be preparing to burst. "And it's not like they're going to take your appendix out in an urgent-care facility," he notes. To be on the safe side, especially if the pain is severe, head for the ER.

While retrieving Christmas decorations, you fall off the ladder and cut your knees while also twisting your ankle. Urgent care would be fine, both doctors agree. As Dr. Till puts it, "it's a simple diagnosis and simple to treat."

Your toddler has a fever of 104. An urgent-care clinic can handle such situations in most cases, Dr. Johnson says, adding that his office can do blood and urine cultures to detect an underlying problem. But don't just focus on the fever, Dr. Till says: "Anything can cause a high fever." If, for example, the child's temperature registers at 101 but the child is also oddly listless and not reacting to pain, "that kid is sick," he notes. "It's not the fever that does it.

"More serious ailments would then be ruled out at the ER.

You have a fever of 104. "We see them all the time," says Ms. King of CareNow. "But it depends on what other symptoms the person is having. It's always iffy; there's always a chance you're going to get sent to the ER." For grown-ups, "there might be underlying symptoms: 'Why is this adult having a 104-degree fever?' For kids, you can definitely just bring them here."

While searching for the turkey deep-fryer in the garage, you get stung by 20 bees. "Twenty bees is an awful lot," Dr. Till says. "You might want to go to the ER."

For smaller swarms, visit the urgent-care clinic. But that's with one exception: "If you're allergic, all bets are off," Dr. Till says. Hives, wheezing and swelling of the tongue or lips are warnings to get to the ER immediately. "If you're really, really allergic," he warns, "you have minutes. Thirty minutes, and you could be dead."

It's Christmas Eve, and your child is throwing up. Again and again. "We'll see them," says Dr. Johnson, of Acute Kids, whose clinic can set up an IV for fluids and try to stop the vomiting. If nothing helps, he says, "we'll call the primary doctor and say, 'Johnny's here and on an IV. Where would you like them to go?' We'd then send them to that ER."

While chopping down a Christmas tree, you lose a digit. "Do not come to the CareNow when you've cut your finger off," says Ms. King, who has seen this happen. "We get them taken care of, assess them and have one of the nurses call 911."

Wrestling with a tough opponent, your 6-year-old son hurts his arm. Dr. Johnson treated that situation on a recent Saturday night, just as they were closing the office. "The mom was upset and worried, so I said, 'Yeah, we're closed, but we'll see you,' " he recalls. The 6-year-old was "screaming and scared to death." Luckily, his arm wasn't broken. The next day, the boy returned, armed with a card and cookies. "He was apologizing for giving us headaches for screaming so loud," Dr. Johnson says. "It was great. I never got cookies in the ER."

CareNow (www.carenow.com ) and PrimaCare ( www.primacare.com) are two of the largest after-hours, walk-in clinics in the Dallas-Fort Worth area. CareNow has 19 locations, with a Cedar Hill clinic opening in December, while PrimaCare has 11 clinics around Dallas. Acute Kids Urgent Care (www.acutekidscare.com) has clinics in Frisco, Plano, McKinney and Flower Mound. Hours vary.

•Most urgent-care clinics accept major insurance plans and operate on a first-come, first-served basis. Not all insurance plans cover every clinic, so be proactive and check with your insurance company. Also, insurance companies may evaluate emergency room visits case-by-case to determine whether they will be covered.