The aim of this study was to compare sleep problems among adolescents who attempted suicide and healthy adolescents who never attempted suicide. Adolescents who attempted suicide (study group, n = 103) and healthy adolescents (control group, n = 59) completed a questionnaire prepared by researchers including demographic factors. In addition, the Pittsburgh Sleep Quality Index (PSQI) and the Epworth Sleepiness Scale (ESS) were administered to both groups. The median age was 16 years and 73% were girls, in both groups. The study group had lower rate of attending to school (88.3% vs. 100%; p = 0.001), academic achievement (45.7% vs. 83.1%; p = 0.001), higher rate of smoking (37.9% vs. 13.8%; p = 0.001), socializing problems (31.1% vs. 3.4%; p = 0.001), and appetite changes (57.3% vs. 39.7%; p = 0.032) than controls. The rate of those with PSQI scores 6 or higher was 53.4% in the attempted suicide group and 37.3% in the control group (p = 0.048). Adolescents, classified as sleepy according to the ESS, did not differ significantly between the groups (p = 0.214). Adolescents who attempted suicide had poor sleep quality. It is crucial to examine the kinds of sleep problems adolescents who have attempted suicide have experienced. Among adolescents attending outpatient clinics with poor sleep quality, PSQI can be a useful screening tool. Those with high scores should be evaluated for suicide risk.