To study the personality characteristics of adults with Asperger syndrome, and investigate the value of self-rating personality inventories, we administered the Temperament and Character Inventory (TCI) to 31 outpatients with Asperger syndrome. The TCI is a self-rating personality inventory that has been validated in the Swedish general population. The results were compared with age- and sex-matched norm groups. Participants with Asperger syndrome scored significantly higher on harm avoidance and lower on self-directedness and cooperativeness. Reward dependence and novelty seeking tended to be low. They also had significantly higher rarity scores, reflecting idiosyncratic perspectives. The most common temperament configurations were 'obsessional', 'passive-dependent' and'explosive'. Character, reflecting conceptual maturity, was poorly developed in the majority of our subjects. The self-ratings of persons with Asperger syndrome thus indicated anxious personalities with coping difficulties in the areas of social interaction and self-directedness, a picture corresponding to the clinical descriptions of Asperger syndrome.