Technical Abstract: Background. There is a need to find ways to increase the physical activity levels and improve the body composition and blood pressure of girls. Methods. Thirty 11-year-old girls were recruited from two after-school programs in Houston, Texas, in spring 2005. Participants from one program (16) were randomly assigned to intervention, the other (14) served as controls. BMI, BMI percentile, waist circumference, and blood pressure were assessed before and after the intervention. Pilates classes were provided free of charge for an hour per day at the intervention site, 5 days a week, for 4 weeks. Four participants wore heart rate monitors during every session and completed enjoyment and perceived exertion questionnaires. Repeated measures analysis of variance with time (within) and group (between) as factors was performed. Results. Mean attendance was 75%, mean heart rate 104 bpm, mean perceived exertion 5.9 (1–10 scale) and enjoyment 4.4 (1–5 scale). There was a significant (P = 0.039) time by group interaction for BMI percentile. Graphs indicated that this difference was influenced by large reductions in the BMI percentile of healthy girls. Conclusions. Girls enjoyed Pilates, and participation for 4 weeks lowered BMI percentile. Pilates holds promise as a means of reducing obesity.