One of the most noticeable problems in autism involves the social use of language such as metaphor and metonymy, both of which are very common in daily language use. The present study is the first to investigate the development of metaphor and metonymy comprehension in autism. Eleven children with autism were compared to 17 typically developing children in a metaphor-metonymy comprehension task. Cross-sectional trajectory analyses were used to compare the development of metaphor and metonymy comprehension using a child-friendly story picture task. Trajectories were constructed linking task performance either to chronological age or to measures of mental age. Children with autism showed an impaired metaphor comprehension in relation to both chronological and mental age, whereas performance on metonymy was delayed and in line with their receptive vocabulary. Our results suggest that understanding of metaphors and metonyms are severely affected at all ages examined in the current study. (Contains 2 tables and 2 figures.)