5/10 members of a North African family (father, 2 male and 2 female siblings) had gynaecomastia, early growth and short final stature. The 8-year-old propositus had advanced bone age, facial acne, gynaecomastia, pubic hair and prepubertal testicular volume. Basal oestrone (E1) was elevated (670 pmol/l) and increased with adrenocorticotropic hormone (ACTH; 826 pmol/l). After human chorionic gonadotropin stimulation testosterone (T) responded normally whereas E1 and oestradiol (E2) remained unchanged. ACTH-dependent adrenal feminization was confirmed by a transient reduction of breast tissue following dexamethasone or cypropterone acetate treatment. Testolactone increased T/E2 (from 5.6 to 20.3) and A/E1 (from 3.4 to 31.4) ratios and temporarily reduced the breast tissue. In conclusion, this is a familial type of adrenal feminization with increased adrenal androgen aromatization. This is the first time that male-to-male and male-to-female transmission has been reported.