Objective To assess dietary costs during a family based pediatric obesity intervention. Design Families were randomized to one of two groups. Dietary and cost data-were collected from a parent or child recalls: at baseline, 6 months and 12 using three 24-hour months. Subjects Thirty-one families with an obese 8- to 12-year-old child entered treatment, with complete dietary data provided from 20 families. Intervention The 20-week behavior modification intervention emphasized increasing diet nutrient-density. Families attended group and individual sessions or group sessions. Main outcome measures Energy intake; percent of energy from protein, fat, and carbohydrate; servings and percent servings from food groups classified by nutrient density; and daily food costs. Statistical analyses performed Mixed analyses of variance, with group as the between-subject factor, and time as the within-subject factor. Results No significant effect of group was found in any analyses. Significant. decreases in percent overweight were observed at 6 and 12 months for children (-10.0 +/- 8.7 and 8.0 +/- 10.3, respectively) (mean standard deviation) and parents (-6.7 +/- 10.3 and -5.3 +/- 14.1). Energy intake for parents and children combined significantly decreased from baseline (1,881 +/- 462) to 6 months (1,412 +/- 284), and 1 year (1,338 +/- 444). Servings from low-nutrient-dense foods significantly decreased from baseline (34.7 +/- 16.2) to 6 months (16.0 +/- 8.6) and 1 year (18.6 +/- 9.2), causing a significant increase in diet nutrient density. Dietary cost did not change at 6 months, but. significantly decreased from baseline to 1 year ($6.77 +/- 2.41 to $5.04 +/- 1.80). Cost per 1,000 kcal did not significantly change. Applications/Conclusions Adopting a lower-energy, nutrient-dense diet did not increase dietary costs over time Consequently, cost should not be a barrier in the adoption of a healthful diet.