CONCLUSIONS: Prone positioning reveals promising results in improving the apnoea-hypopnoea index (AHI) and oxygen desaturation index (ODI) in patients with obstructive sleep apnoea (OSA). OBJECTIVE: To evaluate the effect of the prone position on OSA. METHODS: Thirty-two patients with mild to severe OSA were included in the study. This was a two-night study to evaluate the effect of the prone position on OSA; a first night in a normal bed with optional positioning and a second night on a mattress and pillow facilitating prone positioning. RESULTS: A total of 27 patients, 22 males and 5 females, with a mean age of 51 years, 15 patients with positional OSA (POSA) and 12 patients with non-POSA with a total median AHI of 23 (min 5, max 93) completed the study protocol. The median AHI decreased from 23 to 7 (p < 0.001) and the median ODI from 21 to 6 (p < 0.001). The median time spent in the supine position decreased from 142 to <1 min (p < 0.0001) and the median time in the prone position increased from <1 to 330 min (p < 0.0001). In all, 17 of 27 patients (63%) were considered to be responders to prone positioning, 12 of 15 (80%) with POSA and 5 of 12 (42%) with non-POSA. Five patients did not complete the study protocol due to sleep time <4 h.