A sample of 143 patients, 76 meeting strict DSM-III-R criteria for somatization disorder and 67 somatizers, was studied using Slater's index to measure birth order position. The results showed that birth order position was not associated with the diagnosis of somatization disorder and that sibship position in both groups occurred by chance. Thus, although environmental factors may influence the development of somatization disorder, the expression of environmental influence through birth order is unlikely.