Objective: Evaluate an online coping skills program to prevent mental health problems in children and adolescents from divorced or separated families. Method: Children ages 11-16 (N = 147) whose families had filed for divorce were recruited using public court records. Participants were blocked by risk-score and randomly assigned to either a control (Internet self-study condition, Best of the Net (BTN) or the experimental intervention, Children of Divorce-Coping With Divorce (CoD-CoD), a 5-module highly interactive online program to promote effective coping skills. Program effects were tested on measures of children’s self-reported coping and parent and youth reports of children’s mental health problems. Results: Significant main effects indicated that youth in CoD-CoD improved more on self-reported emotional problems relative to BTN youth (d = .37) and had a lower rate of clinically significant self-reported mental health problems (OR = .58, p = .04). A significant Baseline x Treatment interaction indicated that the 55% of youth with highest baseline problems improved more than those in BTN on their self-report of total mental health problems. A significant interaction effect indicated that CoD-CoD improved youth coping efficacy for the 30% of those with the lowest baseline coping efficacy. For the 10% of youth with lowest parent-reported risk at baseline, those who received BTN had lower problems than CoD-CoD participants. Conclusions: CoD-CoD was effective in reducing youth-reported mental health problems and coping efficacy particularly for high risk youth. Parent-report indicated that, relative to BTN, CoD-CoD had a negative effect on mental health problems for a small group with the lowest risk.