This study examined the nature of repetitive, ritualistic, and compulsive-like behaviors in 50 typically developing children and 50 individuals with Down syndrome (DS), matched on mental age (MA; M = 59.72 months). Parents reported on their children's compulsive-like behaviors-including ritualistic habits-and perfectionistic behaviors, as well as their children's adaptive and maladaptive behaviors. Results indicated that children with DS show similar MA-related changes in compulsive-like behaviors compared to the MA-matched comparison group. Younger children (both typical and DS) exhibited significantly more compulsive-like behaviors than older children. In general, children with and without DS did not differ from each other in terms of the number of compulsive-like behaviors they engaged in, although participants with DS engaged in more frequent, more intense repetitive behaviors. Compulsive-like behaviors were differentially related to adaptive and maladaptive behaviors across the MA and mental retardation groups. The results extend the "similar sequence" model of development to the construct of compulsive-like behaviors, and also suggest that some repetitive behaviors may be among the behavioral phenotype of individuals with DS.