Masturbation in infant girls sometimes leads to doctor visits because parents think the children have a movement disorder, a new study finds.

Don't worry, the researchers say. It's all natural and harmless.

In the study, researchers reviewed a dozen cases of young girls who were referred to pediatric movement disorder clinics between 1997 and 2002 for evaluation of episodic dystonic posturing, characterized by involuntary muscle contractions that force the body into abnormal movements and positions.

After sometimes invasive testing and medication, the neurologists discovered the symptoms were actually normal muscle contractions that accompany masturbation.

"Masturbation is a normal human behavior. It's not harmful to anybody," said study leader Jonathan Mink, Chief of Child Neurology at the University of Rochester Medical Center.

Infant boys who masturbate don't end up at the doctor as often, Mink figures, because the action in boys is more recognizable: They tend to touch their genitals. Girls don't necessarily directly touch their genitals when masturbating. An episode may begin in a car seat or high chair where straps place pressure on the genital area, or they may start when a child is tired or bored.

Viewing the episodes videotaped by parents, Mink determined the children were not suffering from dystonic posturing. One child was distracted out of the episode with the promise of a cookie. Another stopped to play with a toy truck. Children with dystonia cannot respond or be distracted.

The research is detailed in the December issue of the journal Pediatrics.

Mink says pediatricians should ask parents to video-tape the episodes before performing invasive and often expensive tests that could be unnecessary.

He also has some reassuring words for parents:

Masturbation "doesn't portend any sexual deviancy later in life," Mink said. "It's such a common and normal behavior that it's nothing to worry about. It's not appropriate to punish children for it. They associate it with comfort, like thumb-sucking."