Children with Down syndrome (DS) and autism spectrum disorders (ASD) frequently have difficulty riding a two-wheel bicycle. The purpose of this study was to investigate an intervention using an adapted bicycle and individualized instruction to teach 71 youth to ride a standard two-wheel bicycle. Youth with DS (n = 30) and ASD (n = 41) between the ages of nine and 18 years took part in this study. After five days of training, 73.3% of children with DS and 85.4% with ASD successfully demonstrated the ability to ride the bicycle more than 100 feet. Leg strength differentiated riders from nonriders in both groups. For the youth with DS, those who learned to ride were significantly older and heavier than those who did not learn to ride. Participants with ASD who learned to ride were significantly taller and stronger than those with ASD who did not learn to ride a two-wheel bicycle. Implications are discussed. (Contains 2 figures and 4 tables.)