In the present study the response times of 10- to 20-year-old participants with Asperger syndrome (AS) (N=21) of normal intelligence and a control group of typically developing individuals (N=20) were recorded on a new 'advanced' test of theory of mind. This test taps the ability to make mental-state inferences versus physical-state inferences in a story context. The participants with AS were significantly slower than the controls on both tasks. In addition, the differences in response times between mental- and physical-state inference were significantly larger in the AS group than in the control group, suggesting that the clinical group experienced more problems than the controls in making inferences about mental states than about physical states.