AIMS: To examine sleep study findings in children with Prader-Willi syndrome (PWS) referred for polysomnography (PSG) before commencement of growth hormone (GH) and to evaluate the impact of sleep testing on treatment decisions. METHODS: The sleep unit database was used to identify all cases over an 8-year period (2003-2011). Standard overnight PSG was performed in the sleep laboratory. Obstructive sleep apnoea (OSA) was defined by an obstructive apnoea-hypopnoea index >1/h. Age, symptoms of OSA, tonsillar size and body mass index (BMI) Z-score were obtained through chart review. RESULTS: OSA was diagnosed in 15 of 34 (44 ) cases identified. Those with OSA were significantly older (P = 0.009) and more likely to have enlarged tonsils (P = 0.05) than those without OSA. There was no difference in BMI Z-score or the presence of symptoms of OSA. GH was deferred in 13 (38 ) pending treatment for OSA. CONCLUSIONS: OSA was frequently present in children with PWS referred simply to meet the requirement for PSG before starting GH. OSA was more likely in older children and those with enlarged tonsils. GH treatment was deferred in 38 of cases. This study supports routine performance of PSG prior to GH, regardless of clinical history.