A study on traffic noise sleep disturbance was made in an apartment building before and after the installation of noise insulating windows. Three tenants completed a questionnaire each morning one week before and one week after the insulation of windows, and body movements during sleep were recorded during these periods. All persons demonstrated a decrease in the number of body movements after the windows had been insulated and two reported improved sleep quality. The results suggest that subjectively judged sleep quality as well as recordings of bed movements are useful tools for evaluating actions to reduce noise.