OBJECTIVE: To determine the prevalence and characteristics of endocrinopathies at diagnosis of POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes) syndrome. PATIENTS AND METHODS: From January 1, 1960, through June 30, 2006, we identified 170 patients with POEMS syndrome in the Mayo Clinic dysproteinemia database. We abstracted information about endocrine abnormalities from their medical records. RESULTS: Of the 170 patients with POEMS syndrome during the entire study period, the 64 patients seen after 2000 had more complete endocrine evaluations; of these 64 patients, 54 (84%) had a recognized endocrinopathy (38 men; median age, 50 years; interquartile range, 43-59 years). Hypogonadism was the most common endocrine abnormality; 26 (79%) of 33 men had subnormal total testosterone levels, and 10 men had gynecomastia. Among the 35 patients with measured prolactin levels, 7 men and 3 women had elevated levels. Hypothyroidism was noted in 17 men and 11 women. Abnormalities in glucose metabolism were present in 24 (48%) of 50 patients; 16 patients had impaired fasting glucose levels, and 8 were diagnosed as having diabetes. Adrenal insufficiency (defined by an abnormal response of cortisol to stimulation with standard high-dose [250 μg] synthetic adrenocorticotropic hormone) was noted in 6 of 9 patients tested. Fourteen (27%) of 51 patients tested had hypocalcemia. Twenty-nine (54%) of 54 patients had evidence of multiple endocrinopathies in the 4 major endocrine axes (gonadal, thyroid, glucose, and adrenal). CONCLUSION: The high prevalence of endocrinopathy in our study, to our knowledge the largest published series of POEMS cases, calls for a thorough endocrine investigation in patients presenting with this syndrome. © 2007 Mayo Foundation for Medical Education and Research.