Objective: This case-control psychological autopsy study aimed to explore a relationship between sleep disturbances and suicide among Japanese, as well as determine the importance and usability of screening for sleep disturbances in suicide prevention. Methods: A semi-structured interview was conducted with the close family members of 49 adult suicide completers and 145 gender-, age-, and residential municipality-matched living controls. The survey included sections on demographics, sleep disturbances, and mental disorders. Conditional logistic regression analyses were performed to compare sleep disturbance prevalence between the two groups. Results: A significantly higher prevalence of sleep disturbances was found among the suicide group (75.5%) compared to the controls (11.0%) (odds ratio [OR]=21.6, p<. 0.001). The association remained significant after adjusting for mental disorders (OR. = 12.7, p<. 0.001). The population attributable risk percent of suicide associated with sleep disturbances and mental disorders was estimated to be 56.4% and 35.3%, respectively. Conclusions: The study confirmed that sleep disturbances are an important risk factor of suicide, independent of mental disorders. Sleep disturbances accounted for a greater proportion of suicide cases than did mental disorders in the Japanese population given the higher prevalence, and could thus be considered an important target in suicide prevention in Japan. © 2014 Elsevier B.V.