This study was the first nationwide population-based study to estimate the prevalence rates of sleep disturbance and hypnotic medication use in the general Japanese adult population. In 1997, 2, 800 Japanese adults aged 20 years and over were randomly selected from the 1995 Census and 1, 871 were examined using the Pittsburgh Sleep Quality Index. The respective estimated overall prevalences of insomnia (INS), difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS), poor perceived quality of sleep (PQS) and hypnotic medication use (HMU) were 17.3%, 8.6%, 12.9%, 17.8%, and 3.5% in males and 21.5%, 12.6%, 16.2%, 20.2% and 5.4% in females. Among males, DIS (OR=2.76) and PQS (OR=2.12) were associated with never having married. DMS was associated with being 60 years and older (OR=2.68) or divorced/separated (OR=3.74). Among females, DMS was associated with being widowed (OR=1.65), unemployed (OR=1.60), 40 to 59 years old (OR=0.57) or never having married (OR=0.39). DIS was associated with being widowed (OR=1.67) or unemployed (OR=1.58). HMU was associated with advancing age (OR=8.26-10.7), being widowed (OR=2.12) or never having married (OR=2.84). PQS was associated with advancing age (OR=0.63-0.50). Our study showed sleep disturbance and hypnotic medication use were prevalent among Japanese adults and some sociodemographic factors contributed to them. J Epidemiol, 2000 ; 10 : 79-86