Fibrous dysplasia (FD) is a rare disease caused by a sporadic postzygotic missense mutation that leads to abnormal fibroblast proliferation, defective osteoblast differentiation, and increased bone resorption. It may affect one or several bones. Both the mono-ostotic and polyostotic types may be associated with hyperfunctional endocrinopathies and hyperpigmentation of the skin (café-au-lait spots) in the so-called McCune-Albright syndrome (MAS). Due to its rarity, only a few case series are available, making it difficult for most clinicians to judge the severity of the disease. To improve our knowledge of FD, we reviewed all cases of FD treated at our department of endocrinology. Among 26 patients, 17 (65 %) had polyostotic FD, with four being diagnosed with MAS. Patients with polyostotic FD were diagnosed at an earlier age (median 13, range 0.5-64 years) than patients with the mono-ostotic form (median 21, 1-70 years). Craniofacial bones were affected in 80 % of cases, and 66 % complained of bone pain at the affected site, with no difference between patients with mono- and polyostotic FD. Two patients with mono-ostotic and three with polyostotic FD had cranial nerve impairments. Fourteen underwent, at least, one surgery, six (67 %) with mono-ostotic and eight (47 %) with polyostotic FD. Most received treatment with bisphosphonates, but therapy did not result in any clear relief of symptoms or radiological improvements. In conclusion, bone pain is common in patients with FD. The severity of the disease depends on affected bones as mono-ostotic may be as debilitating as polyostotic FD. In our case series, bisphosphonate treatment did not show clear beneficial effects.