Neuropsychological studies in myasthenia gravis (MG) were undertaken to prove the central nervous involvement. However, they still produce contradictory results. In the present study, a battery of cognitive measures was administered to examine global cognitive functioning, verbal learning, attention, executive function and motor performance. Analysis of partial scores in verbal learning and response fluency trials did not reveal fatigue effect in MG patients. It was shown that in tasks requiring motor, and particularly oculomotor, involvement, the muscle fatigue could account for the deficits observed. Thus, impaired performance on some cognitive measures in MG should be interpreted as an effect of muscle fatigability rather than central nervous system involvement.