The purpose of this study was to review the phenotypic and endocrine features of a series of patients with ambiguous genitalia or sex-reversal due to gonadal dysgenesis (GD) and to analyse the impact of these on the decision about sex of rearing. This study is a retrospective analysis of 22 patients with GD treated between 1964 and 1994. We assessed external genitalia, internal genital structures, gonadal morphology (n=22), basal and human CG (hCG) stimulated serum testosterone levels (n=11) and serum gonadotropin levels (n=13) in patients with GD. Basal and hCG stimulated testosterone levels were also measured for 43 control patients. There were no significant associations or correlations between internal or external genital phenotype, endocrine function and gonadal morphology. There was a significant association between sex of rearing and external genitalia (P=0.03). Patients with gonadal dysgenesis had significantly lower stimulated/basal testosterone levels than the controls (P=0.0001). Given that the clinical features of various forms of GD overlap considerably, gonadal biopsy should remain the investigation of choice when attempting to define the pathology.