CONTEXT: Guidelines advise lifelong radiological followup for asymptomatic pituitary adenomas (PITs) because of the risk for growth and subsequent visual field defects. In the context of multiple endocrine neoplasia type 1 (MEN1) an even more comprehensive screening is advised because PITs are presumed to manifest more aggressive behavior. We studied the long-term course of MEN1-related PITs, which may be used as a model for sporadically occurring PITs. OBJECTIVE: The aim of our study is to assess the results of systematic pre-symptomatic PIT screening and subsequent long-term followup of PITs with emphasis on nonfunctioning microadenomas diagnosed by screening. PATIENTS AND METHODS: A cohort study was performed using the Dutch national MEN1 database, including greater than 90% of the Dutch MEN1 population older than 16 years (n = 323). MAIN OUTCOME MEASURES: Screening results, natural course, and effects of treatment of PIT were assessed. RESULTS: PIT was diagnosed in 123 patients with MEN1 (38.1 %), of whom 66 were diagnosed by MEN1-related screening. Ninety-one percent of the nonfunctioning PIT detected during screening (n = 35), did not require intervention during followup (median, 6.0 y). Three microadenomas showed limited growth but did not progress toward macroadenomas. Both screening-detected and prevalent prolactinomas (n = 52) responded well to treatment with dopamine agonists. CONCLUSION: Systematic presymptomatic screening for PIT in patients with MEN1 predominantly results in detection of nonfunctioning microadenomas. Prolactinoma in patients with MEN1 responded well to medical treatment. Microadenomas grew only occasionally and after many years without clinical consequences. Frequent magnetic resonance imaging followup of nonfunctioning microadenomas in the context of MEN1 and sporadically occurring PITs therefore seems debatable.