Although pragmatic deficits are well documented in autism, little is known about the extent to which grammatical knowledge in this disorder is deficient, or merely delayed when compared to that of typically developing children functioning at similar linguistic or cognitive levels. This study examines the knowledge of constraints on the interpretation of personal and reflexive pronouns, an aspect of grammar not previously investigated in autism, and known to be subject to differential developmental schedules in unimpaired development. Fourteen children with autism (chronological age = 6-17 years, "M" = 11) showed some difficulties comprehending personal pronouns, no different from those observed in two groups of younger controls matched on nonverbal IQ or receptive grammar, but in line with the reported pragmatic deficits and general language delay in this population. However, their interpretation of reflexives was significantly worse than that of the control children. This pattern is not evidenced at any stage of typical development, revealing an impaired grammatical knowledge in our sample of children with autism, and is argued not to be due to a general language delay or cognitive deficits.