Eight women with amenorrhea, galactorrhea, and hyperprolactinemia, of whom six had macroadenomas and two had microadenomas, were treated with conventional (cobalt-60) external radiotherapy, and their progress was monitored for eight to 15 years. Normoprolactinemia was established in five of these patients after two to 13 years (median, nine years). A recurrence was treated surgically in one patient, and stable prolactin values and roentgenographic features have been maintained in two patients. Hypopituitarism has developed in only one patient to date, and no other complications of radiotherapy have been observed. These findings, together with the few previous reports on the long-term effects of radiotherapy on macroprolactinomas, have been compared with the long-term results following surgery or dopamine agonist therapy. The normalization of prolactin values is considerably delayed following radiotherapy compared with the other two therapeutic modalities. However, radiotherapy affords permanent normalization without recurrence in a larger percentage of patients than does surgery and avoids the considerable ongoing cost and inconvenience of daily drug ingestion. The long-term development of hypopituitarism appears to be an acceptably small risk of radiotherapy. Thus, conventional radiotherapy is an attractive treatment option, particularly for macroprolactinomas; adjunctive bromocriptine can be used while awaiting the longer-term benefits of radiotherapy.