• The relationship between psychiatric impairment and disability due to somatic complaints was studied in 859 women adopted at an early age by nonrelatives in Sweden. The clinical data were derived from the comprehensive registrations for all medical treatment and sick-leave compensation that are kept about Swedish residents by the National Health Insurance Board. The adoptees were compared with nonadopted controls who were individually matched for social and demographic variables. We identified a somatization syndrome that is consistently associated with psychiatric impairment and repeated brief periods of disability with chief complaints of headache, backache, and abdominal distress on different occasions. A method for clinically distinguishing "somatizers" from other women was derived in one sample and was shown to have a classification accuracy of 97% in a replication sample. Somatizers accounted for 36% of all cases of psychiatric disability and 48% of all sick-leave occasions in adopted women. Compared with nonadoptees, there was an excess of somatizers in adoptees, a population known to have an excess of biological parents who are criminal and/or alcoholic.