BACKGROUND Compared with their peers with nondivorced parents, adolescents with divorced parents are more likely to have mental health problems, drop out of school, and become pregnant. The long-term effects of intervention programs for this population are unknown. OBJECTIVE To evaluate the long-term effectiveness of 2 programs designed to prevent mental health problems in children with divorced parents. METHODS Six-year follow-up of a randomized controlled trial of 2 intervention programs (mother program: 11 group and 2 individual sessions; mother plus child program: mother program and 11 group sessions for children) and a control condition (books on postdivorce adjustment), which was conducted in a large metropolitan US city from April 1998 through March 2000. METHODS A total of 218 families (91% of the original sample) with adolescents aged between 15 and 19 years were reinterviewed. METHODS Externalizing and internalizing problems, diagnosed mental disorders, drug and alcohol use, and number of sexual partners. RESULTS Eleven percent of adolescents in the mother plus child program (95% confidence interval [CI], 3.8%-18.2%) had a 1-year prevalence of diagnosed mental disorder compared with 23.5% (95% CI, 13.8%-33.2%) of adolescents in the control program (P =.007). Adolescents in the mother plus child program had fewer sexual partners (mean [SE], 0.68 [0.16]) compared with adolescents in the control program (1.65 [0.37]; P =.01). Adolescents with higher initial mental health problems whose families were in the mother plus child program had lower externalizing problems (P =.007) and fewer symptoms of mental disorder (P =.02) compared with those in the control program. Compared with controls, adolescents whose mothers participated in the mother program and who had higher initial mental health problems had lower levels of externalizing problems (P<.001); fewer symptoms of mental disorder (P =.005); and less alcohol (P =.005), marijuana (P =.02), and other drug use (P =.01). CONCLUSIONS In adolescents of divorced parents, the mother program and the mother plus child program reduced symptoms of mental disorder; rates of diagnoses of mental disorder; levels of externalizing problems; marijuana, alcohol, and other drug use; and number of sexual partners.