Gastroenteropancreatic neuroendocrine tumors (GEPNET) are rare tumors that may be sporadic or develop as part of multiple endocrine neoplasia type 1 syndrome (MEN1). The aim of the present study was to report the experience of a Brazilian multidisciplinary outpatient neuroendocrine tumor clinic regarding the clinical diagnosis of MEN1 in a cohort of GEPNET patients. Patient data, including clinical characteristics and the lag time from the onset of symptoms to diagnosis of the first tumor, and further lag time until the diagnosis of MEN1, were retrospectively reviewed. Among 44 GEPNET patients, 6 had a clinical diagnosis of MEN1. Primary hyperparathyroidism and GEPNET were present in all patients in the cohort, and pituitary neuroendocrine tumors were present in 33.3%. The median time interval from the onset of initial symptoms to the diagnosis of the first tumor was 42 months (range, 0-204 months). The median time interval between the diagnosis of the first tumor and the diagnosis of MEN1 was 22 months (range, 1-109 months). The prolonged lag time between the onset of initial symptoms and MEN1 diagnosis may result in substantial morbidity and loss of opportune interventions for the patients. Therefore, greater efforts should be made to shorten these times and improve the care of patients with MEN1. Patients and methodsPatients. This is a retrospective review of clinical data obtained from all patients who had a clinical diagnosis of