A Central Nervous System (CNS) acetylcholine receptors involvement in Myasthenia Gravis (MG) has been suggested but never fully demonstrated. On the other hand, although the question concerning the neurotransmitters connected to REM sleep is still unsettled, the importance of acetylcholine as a neurotransmitter involved in the maintenance of this sleep stage has been outlined. The spontaneous night sleep organization has been studied in 9 male subjects with MG and results are compared with those obtained in normal subjects matched for age and sex. Statistically significant differences have been found: 1) slow-waves sleep better represented in MG patients; 2) average REM period length shorter in MG patients; 3) instability of the EEG consisting in a tendency toward lightening of sleep. These findings may confirm the presence of a disturbance in the CNS cholinergic activity of MG patients.