Day time somnolence or excessive snoring, or both, occurred in five out of 11 patients with acromegaly. All five had episodes of sleep apnoea, and three had the sleep apnoea syndrome. Growth hormone concentrations were higher (p less than 0.025) in these patients than in the six patients without these symptoms. One patient with daytime somnolence and one asymptomatic patient had flow loop evidence of upper airways obstruction. Two of the patients with the sleep apnoea syndrome had cardiomegaly. Sleep apnoea appears to be common and clinically important in acromegaly, and it may be central, obstructive, or mixed. Polygraphic nocturnal monitoring is indicated to assess these patients properly.