Obesity is the most common chronic disease of childhood. Data from 100 children in Baltimore, Maryland. The mean age of our population was 11.8 years and 56% were overweight (body mass index>85 percentile). Most (96%) knew how to ride a bike and 80% reported owning a bike. Children who rode a bike just once a week or less were the most likely to be overweight. This association was stronger than for all other dietary and activity practices. Riding a bicycle at least 2 or more days during the week is associated with a decreased likelihood of being overweight during childhood.