The aim of this prospective study was to determine if sleep disturbances and nightmares are associated with increased risk of repeat suicide attempt. Patients (n=165) aged 18-68 years who were admitted to medical or psychiatric wards after a suicide attempt completed an initial interview; 98 of these took part in a 2-month follow-up interview. The Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) and two self-report instruments, the Uppsala Sleep Inventory and the Comprehensive Psychopathological Rating Scale (CPRS) Self-Rating Scale for Affective Syndromes, were administered both at baseline and follow-up. Data concerning repeat suicide attempts within 2 years were obtained from hospital records. Analyses were performed using Student's t-test, chi-square test, and logistic regression. In total 42 patients (26%) made at least one repeat suicide attempt within 2 years. While neither difficulties initiating/maintaining sleep nor early morning awakening at baseline predicted repeat attempt, having frequent nightmares did (OR=3.15). The risk was further heightened when nightmares were reported at both baseline and 2-month follow-up (OR=5.20). These associations remained after adjusting for sex, axis-I DSM-IV diagnoses, and self-reported depression and anxiety symptom intensity. Our findings suggest that nightmares might constitute a marker for increased risk of suicidal behavior.