P>Context and Objective Somnolence and obesity are prevalent in craniopharyngioma patients. We hypothesized that somnolence was because of obstructive sleep apnoea in craniopharyngioma patients. Design, Patients and Measurements We assessed prevalence of somnolence and sleep apnoea in 28 craniopharyngioma and 23 obese controls attending a tertiary referral centre, by means of the Epworth Sleepiness Score (ESS) and polysomnography. All subjects with sleep apnoea were offered continuous positive airway pressure therapy (CPAP) or modafinil. All craniopharyngioma patients, with unexplained somnolence, were offered modafinil. Results Somnolence was reported by 20/28 (71 center dot 5%) craniopharyngioma patients and 4/23 (17%) obese subjects (P < 0 center dot 001). Median ESS was 7 center dot 5 (IQR 6, 10 center dot 7) in craniopharyngioma patients and 4 center dot 0 (4,8) in controls, P < 0 center dot 01. Eleven somnolent craniopharyngioma patients had obstructive sleep apnoea, in whom treatment led to a reduction in ESS by 6 center dot 4 +/- 1 center dot 4, P = 0 center dot 01. Among the remaining nine patients, five were offered modafinil therapy, of whom four had benefit, three were not compliant with hormone replacement, and one died before intervention. There was no difference in the prevalence of obstructive sleep apnoea between craniopharyngioma (n = 13, 46%) and obese subjects (n = 14, 61%, P = 0 center dot 4). Body mass index (BMI) does not correlate with apnoea hypopnoea index [apnoea - hypopnoea index (AHI), r = 0 center dot 25, P = 0 center dot 08], which suggests that obesity alone does not explain the prevalence of sleep apnoea in craniopharyngioma patients. Conclusions Somnolence is common in craniopharyngioma patients and in the majority is because of obstructive sleep apnoea. An additional group of somnolent craniopharyngioma patients benefits from modafinil.