Male pseudohermaphroditism (MPH) is a disorder of sexual differentiation whereby the external genitalia are at variance with a male karyotype and the presence of testes. Abnormalities of Leydig cell function are an important cause of MPH, but postnatal age must be considered when interpreting the testosterone response when HCG stimulation is used as a diagnostic test. Androgen insensitivity is also a common cause of MPH; the specific defect in androgen receptor function is currently the subject of intense study, using a combination of biochemical assays and molecular analysis of the androgen receptor gene. The treatment of MPH is influenced by genital tissue responsiveness to androgens and the technical complexity of reconstructive surgical procedures. There is a need for information on the outcome of MPH treatment regarding pubertal development, sexual performance and fertility.