Routinized and compulsive-like behaviors (RCB) are common in typically developing children and in children and adults with Down syndrome, but what functions do they serve? Parents completed questionnaires for RCB, behavior problems, and adaptive behaviors. Children who had Down syndrome had significantly higher levels of RCB than did the typically developing children at all MAs; RCBs were positively associated with adaptive behaviors for younger MA and CA groups, but not older MA children and all adults with Down syndrome. For children with Down syndrome and MAs over 5 years and all adults, RCBs were associated with behavior problems. We concluded that RCBs support developmental progress for all children with MAs less than 5 years, but may have different functions for older individuals.