Impairments in imitation are present in young children with autism spectrum disorders (ASD), but the onset of these impairments is unknown. The present study investigated the developmental trajectories affiliated with various types of imitation. Imitative performances in infancy were observed in a prospective design, and retrospectively compared between ASD and typically developing (TD) infants. The results indicated that infants who later presented the symptoms of ASD showed less imitation at 13 months of age, but not at 11 months. Both of TD and ASD infants imitated more object manipulations than gestures and meaningless movements, and gestures were more frequent than meaningless movements. Imitation impairments in ASD appear to be delayed instead of being atypical. Our findings can be used in assessments of ASD before 18 months of age.