Twenty-eight consecutive patients with multiple sclerosis (MS) were clinically evaluated to determine the presence of sleep-related disorders. There were 12 males and 16 females aged between 22 and 67 with disability ranging between 1.5 and 8.5 on Kurtzke extended disability status score (EDSS). Fifteen patients (54%) reported sleep-related problems. These included difficulties initiating sleep and/or frequent awakenings due to spasms or discomfort in the legs (8 patients), difficulty in initiating or maintaining sleep (3), habitual snoring (4) and nocturia (1). All-night oximetry was performed and the tracings analysed for the number of dips in oxygen saturation (SaO2) or more than 4%. Three patients showed significant sleep-related oxygen desaturation (> 5 dips of > 4% SaO2/h). Subsequent polysomnography performed in 2 of the 3 patients with significant oxygen desaturation confirmed the presence of sleep apnoea. MRI analysis of brain stem regions showed abnormalities in 20/22 cases. The 3 patients showing nocturnal oxygen desaturation had MRI brain stem lesions, but their locations were variable and their general appearance not different from that seen in the 17 without sleep apnoea. Sleep disturbance in MS is common but poorly recognised. It is usually due to leg spasms, pain, immobility, nocturia or medication. It is much less commonly associated with nocturnal respiratory insufficiency.