The objective of this study was to determine predictors of repeated suicide attempts in young people, focusing on psychiatric illness. A longitudinal population-based register study of all adolescents born in Denmark between 1984 and 2006 was conducted. Greater numbers of hospitalizations, psychiatric diagnoses, and psychopharmacological medications prescribed to youth before and after the index attempt were risk factors for repeated suicide attempts. Parental diagnoses and drug prescriptions following a child's first suicide attempt moderated the risk of repeated attempts. Psychiatric illness is a strong predictor of repeated suicide attempts in young people, and those with co-morbid diagnoses are at increased risk of repeated suicide attempts. Treatment of psychiatric illness in the parents after their child's first suicide attempt is a potential protective factor.