Clinical and anecdotal reports suggest that people with autism have a poor intuitive sense of time. However, almost no relevant research has been reported. The research reported here was designed to begin to remedy this situation, using paradigms from the literature on normal development. Specifically, the ability to utilize a diachronic perspective was investigated, the diachronic perspective being defined in terms of the ability to use temporal concepts and knowledge in thinking and reasoning. Twenty-three children and teenagers with autism were compared with 23 age and ability matched controls on tests of (1) diachronic Tendency (comparable to what has been termed ?mental time travel?); (2) qualitative Transformation (understanding that objects and situations change qualitatively over time); (3) temporal Dissociation (the ability to dissociate the temporal succession of one set of changes from the temporal succession of another, related, set of changes); and (4) dynamic Synthesis (the ability to conceive of a temporal succession of states or events as compressed into a single superordinate event). The materials and methods used closely resembled those used to test typically developing children. Results showed that the experimental participants were markedly impaired on diachronic Tendency, qualitative Transformation, and dynamic Synthesis and showed a trend towards impairment on temporal Dissociation. Performance was not related to chronological age, verbal ability (British Picture Vocabulary Scale) or non-verbal ability (Ravens Matrices) in the experimental group. The same was true for the controls except that in this group non-verbal ability correlated with performance on temporal Dissociation. Children and teenagers with autistic spectrum disorders have impaired ability to think and reason using temporal concepts and knowledge. This may reflect a specific impairment in processing time unrelated to general ability. Some of the results of this empirical research have been presented at the British Experimental Psychology Society (Boucher & Pons, 2003). This empirical research is still running. With Jill Boucher (Warwick University).