During the last four years 12 Prolactin (PRL) secreting adenomas whose first clinical manifestation appeared before the age of 15 years have been studied. The first signs were a decreased growth rate and arrest of pubertal development in 4 girls and 2 boys in whom the adenoma occurred before or during puberty. In the other six cases (5 girls and 1 boy) the first signs were secondary amenorrhea and galactorrhea in girls and in the boy gynecomastia followed by galactorrhea. Symptoms of the tumour (headaches, and visual disturbances) were almost invariable (11/12) and led to the diagnosis in two cases. Plasma PRL levels were always elevated (80 to more than 5,000 ng/ml) and did not rise in response to TRH. 11 out of 12 were large tumours and pituitary tomography showed that tumour was circumscribed in five cases and invasive in the other seven. The prognosis is related to the short term outcome. The condition may be cured by surgery only (25% cases only) or by surgery and bromocriptine.