2933 respondents resident at 53 sites in Greater London were interviewed to obtain data with respect to sleep disturbance. The questionnaire employed covered health and sleep experience, actions taken to ensure sleep, believed causes of disturbance, and procedures aimed at reducing noise within the bedroom. Noise levels were measured at the dwelling façades over the hours of 22.00 to 06.00 and computed values for a variety of physical measures covering different parts of the night correlated with respondents' reports. Although personal factors such as age, sex, occupational class, and state of health all contribute to sleep disturbance, the chief source appeared to be traffic noise. Highly significant predictions of disturbance related to traffic noise, measured as dB(A) L10 over 22.00-06.00 hours, were yielded by reports of undisturbed sleep taking into account reports of sleeping at the front or rear of the dwelling and whether bedroom windows were open or closed in summer.