Dr. Schrader said he and his colleagues had been astounded by the results. Even though they were skeptical about chronic whiplash, they had expected that a few genuine cases would turn up. But not one did, not even among the 16 percent of drivers who recalled having neck pain shortly after their accidents.

When the subjects were finally told the real purpose of the study, they were amazed to learn that anyone could think that an accident that had happened more than a year ago could still be causing health problems. Dr. Schrader recalled, "They said, 'Headaches? Why don't you ask me why after two years I still haven't got the spare part for my bumper?' "

When the findings were publicized in Norway, Dr. Schrader said, the leader of the whiplash patients' organization threatened to sue him. Questions were also raised about whether the research had been financed by the insurance industry. The answer is no, he said; the money came from his university.

Dr. Schrader said he did not doubt the existence of short-term whiplash injuries but did doubt the validity of chronic cases. His conclusions agree with those of a study, published a year ago in the journal Spine, that concluded that about 90 percent of whiplash injuries healed on their own in days or a few weeks and needed very little treatment.

But other injuries may persist, physicians say. "You can't conclude from this small study that whiplash syndrome doesn't exist," said Dr. Paul McCormick, an associate professor of neurosurgery at the Columbia University College of Physicians and Surgeons. "But the researchers are right on in questioning the prevalence."

Dr. McCormick said that some patients sustained lasting, identifiable injuries from whiplash but that milder cases were hard to diagnose. "We don't have objective criteria for those," he said. "There's no lab test." Soft-tissue injuries do not show up clearly on X-rays or in M.R.I. scans. The diagnosis is based on symptoms reported by the patient, who may or may not be reliable. "We have to be careful as scientists and human beings not to see everyone as scheming and lying," Dr. McCormick said.

Other specialists also say that some chronic whiplash cases are real. "I've seen patients 25 years down the road still having problems," said Dr. Barry August, a dentist who is a director of the head and facial pain-management program at New York University Medical Center. The condition can become chronic, he said, when people alter their posture to relieve the pain of injured tendons and muscles. "They begin to compensate," he said, "and these compensations also cause problems."