The study explores the common clinical impression and previously reported finding by Hebebrand et al. (7) of reduced body weight in male children and adolescents with Asperger's disorder (AD). Body weight and height of 36 consecutively admitted male patients with AD were retrospectively assessed for the calculation of body mass indices (BMI, kg/m2). The BMIs were transformed to percentile ranks and plotted into BMI-centiles representative for the German population. In addition, comorbid psychopathology was assessed to explore a possible relationship between associated psychopathology and body weight. The mean BMI-centile of all patients was 34.7 +/- 31.8 and, thus, differed significantly from the mean centile of an age- and gender-matched psychiatric control group, which was 52.7 +/- 28.3. Thirteen patients had a BMI below the 10th centile and five even below the third. Three of the latter presented with disturbed eating behaviour. Altogether four patients showed disturbed eating behaviour. They had a significantly lower mean BMI-centile than the rest of the group. The BMI-centiles of patients with other additional psychopathology did not differ significantly from the mean percentile of the whole cohort. The results clearly show an increased risk for underweight and disturbed eating behaviour in patients with Asperger's disorder which should be evaluated in further studies.