This study investigated the prevalence of snoring and symptoms of sleep breathing-related disorders in the multi-ethnic population of Singapore (3 million people, comprising 75% Chinese, 15% Malay and 7% Indian). A multistaged, area cluster, disproportionate stratified, random sampling of adults aged 20-74 yrs was used to obtain a sample of 2,298 subjects (65% response), with approximately equal numbers of Chinese, Malay and Indian and in each 10 yr age group. An interviewer-administered field questionnaire was used to record symptoms of snoring and breathing disturbances during sleep witnessed by a room-mate and other personal and health-related data. The weighted point estimate (and 95% confidence interval) of the whole population prevalence of snoring was 6.8% (53-83). There were pronounced ethnic differences among Chinese, 6.2% (4.4-8.1); Malay, 8.1% (6.1-10.2) and Indian, 10.9% (85-13.4). The minimum whole population prevalence by the most restricted symptom criteria for defining sleep breathing-related disorder was 0.43% (0.05-0.8%). Similar marked ethnic differences in rates were observed using various symptom criteria. The ethnic differences in sleep breathing symptoms paralleled the differences in body mass index, neck circumference and hypertension, but statistically significant differences remained after adjustment for sex, age and these known associated factors. Marked ethnic differences in snoring and sleep breathing-related disorders were observed in Chinese, Malays and Indians in Singapore, which were only partly explained by known factors of sex, age and body habitus.