A large proportion of narcoleptic patients have periodic leg movements (PMS) in sleep. The contribution of these movements to the nocturnal sleep disturbance observed in narcoleptics remains a controversial issue. The aim of the present study was to look at the sleep organization of narcoleptic patients before and after suppression of periodic leg movements with L-dopa. L-dopa and a placebo were administered in a double-blind fashion to six narcoleptic patients. Each treatment period lasted 2 weeks and the treatment order was reversed for one-half of the subjects. The effects of L-dopa and placebo were evaluated by polysomnography. A significant reduction of PMS was seen after treatment with L-dopa, but this treatment did not improve sleep organization. On the contrary, L-dopa increased wake time after sleep onset. This result supports the hypothesis that PMS does not play a major role in the nocturnal sleep disruption observed in narcolepsy. It also supports the hypothesis that dopaminergic mechanisms play a role in the physiopathology of PMS.