Aim: The aim of the study was to develop and implement an obesity and weight gain prevention program targeted to a high-risk group. Method: Women, 18-28 years old, with at least one severely obese parent, were randomized to the intervention or control group of the 'Health Hunters' program. During 1 year of follow-up, the intervention group received an individualized behavioral program focusing on food choice, physical activity and other lifestyle factors. Anthropometric measures, DXA-based body composition and fitness levels were measured at baseline and after 1 year. Self-reported changes in obesity-related behaviors were also assessed. Results: Baseline examinations were conducted in 40 women, of whom 30 completed follow-up examinations 1 year later. Pregnancy was the most common reason for failure to complete the study. Compared to the control group (which gained weight), the intervention group displayed significant improvements in body weight, body mass index, waist circumference, waist-to-hip ratio and self-reported physical activity. Changes in body composition, although not significant, suggested that the intervention tended to be associated with improved body composition. Further analysis of changes in diet and fitness in relation to concurrent weight changes indicated that the strongest 'protective' associations were for energy percent protein, fiber density and fitness. Conclusion: Pilot data from the Health Hunters obesity prevention program indicates that it is effective in high-risk young women with familial predisposition for obesity.