Forty patients were evaluated using sleep studies for assessment of possible sleep apnoea/hypopnoea syndrome. Twenty-six patients had significant sleep apnoea based on polysomnography. Most of the patients with this syndrome had at least two of the three major symptoms of obstructive sleep apnoea-witnessed apnoeas, heavy snoring, and excessive daytime somnolence. The most common associated medical illnesses were hypertension (47%), chronic obstructive airways disease (16%), respiratory failure (15%), and allergic rhinitis (12%). All 26 patients with sleep apnoea/hypopnoea syndrome were treated with either continuous positive airways pressure or bilevel positive airways pressure with significant improvement. Minimum percentage arterial oxygen saturation increased significantly, with a median difference of 25.5 (interquartile range, 10 to 36; P<0.01) and the apnoea/hypopnoea index decreased significantly with a median difference of 23.0 (interquartile range, 15 to 44; P<0.01). The clinical features of this syndrome in Hong Kong are similar to those reported in the West.