Previous series of pediatric pituitary adenomas have been small and have not been analyzed by age group. We analyzed the frequency, manifestation, course, and biology of these tumors before, during, and after puberty in 136 children younger than 20 years old at surgery, identified by review of 2230 patients treated from 1969 to 1993. Tumors were classified by clinical phenotype. Adrenocorticotropic hormone-releasing adenomas were most common before puberty, and prolactinomas were most common during and after. The frequencies of adrenocorticotropic hormone-releasing adenomas, prolactinomas, and endocrine-inactive adenomas differed from those in adults. Growth arrest was common with all types except growth hormone (GH)-releasing adenomas; menstrual irregularities were common with all but adenomas causing Nelson syndrome. Among girls with prolactinomas, the preoperative duration of primary amenorrhea was longer than that of other symptoms. Tumor size differed by adenoma type. Serum hormone levels shortly after surgery correlated with the recurrence of prolactinomas and GH-releasing adenomas. The prolactinoma size correlated with the maximum preoperative serum prolactin level; boys had larger tumors and higher preoperative and postoperative prolactin levels. We conclude that pediatric pituitary adenomas vary in size, age at symptom onset, and frequency before, during, and after puberty. Most adenomas can cause menstrual irregularities, and primary amenorrhea should prompt investigation of the sella. Growth arrest is common with all adenomas except GH-releasing adenomas. Serum prolactin and GH levels measured at 1 to 5 days after surgery indicate the risk of recurrence of prolactinomas and GH-releasing adenomas, respectively.