We investigated to what extent the initial outpatient clinical findings could predict the results of in-patient nocturnal pulse oximetry in 108 snorers. 30.6% of the patients had oxygen desaturation index (ODI) > or = 5. The lowest SpO2 dip was strongly correlated to ODI (R2 = 0.729). Body mass index (BMI) and FVC were independently correlated to ODI. Relative risk of nocturnal hypoxemia was 3.2 at BMI > 32.0 kg/m2, and 3.0 at FVC < 87% of predicted value, compared with the whole referred group of snorers. Sensitivity of reported apnoea was 0.91, but specificity was only 0.21 with respect to hypoxaemia. Age, sex, hypersomnolence, morning headache, nasal congestion, smoking and consumption of alcohol or sedatives were not predictive of nocturnal hypoxaemia, neither were erythrocyte volume fraction, PaO2, nor PaCO2.