Patients with myotonic dystrophy frequently complain of hypersomnolence, a symptom which seriously restricts their social life. The pathogenesis of this symptom is a matter of debate: it has been attributed to both alveolar hypoventilation and pathological changes in the brainstem. As selegiline has been shown to reduce the number of sleep attacks in nacrolepsy, we tested whether hypersomnolence in myotonic dystrophy would respond to the same treatment. Ten patients with myotonic dystrophy received selegiline/placebo (20 mg daily) in a double-blind crossover trial. We monitored daytime sleepiness by means of a multiple sleep latency test. Treatment appeared to be well tolerated but did not alter hypersomnolence in myotonic dystrophy. Further studies to assess the effect of higher doses of selegiline are warranted.