Group parent-training interventions for the treatment and prevention of externalizing problems in young children have been empirically validated almost exclusively with mother-only groups or with groups where the majority of participants are mothers. One reason for this focus has been the difficulty in attracting fathers to parent-training groups. In order to examine the idea that father-only groups would produce high rates of acceptance and attendance among fathers, we randomly assigned 39 ethnic minority fathers of 3 to 5-year-old children attending Head Start preschool either to an 8-week father-only parent-training intervention or to a no-treatment control group. Initial interest and attendance was strong, although dropout became a major problem, with 70% of fathers assigned to the experimental group attending fewer than half of the sessions. While statistical power was too low to uncover significant treatment effects, some trends nonetheless support the utility of this approach. Father and teacher reports, but not mother reports, suggest that children whose fathers were in the experimental group demonstrated fewer behavior problems than children whose fathers were in the untreated control group. The intervention did not produce significant effects on father discipline skills, nurturance toward their children, or fathers' contributions to childrearing activities. Interestingly, there are indications that the intervention had a negative impact on the marital/cohabiting relationship. This pilot study is a first step in understanding how to effectively engage fathers in parent training. (author abstract)