OBJECTIVE: To investigate if vitamin D deficiency is more prevalent in patients with Paget's disease of bone (PDB) than in age-matched controls. SUBJECTS AND METHODS: We measured serum 25-OHD in 28 untreated patients with PDB and two control groups: 284 elderly men from an ongoing cohort from our department, and 151 postmenopausal women seen in our outpatient clinic for routine medical evaluation. RESULTS: The mean ± SD serum 25-OHD was significantly lower in subjects with PDB (23.76 ± 6.29 ng/mL) than in the control groups of elderly men (27.86 ± 13.52 ng/mL) and postmenopausal women (30.30 ± 9.59 ng/mL), p = 0.015. The prevalence of vitamin D deficiency considering a cut-off point of serum 25-OHD < 30 ng/mL was 85.7% in patients with PDB, and in elderly men and postmenopausal women it was 66.7 % and 54.3%, respectively (p < 0.001). CONCLUSION: These results suggest a high prevalence of hypovitaminosis D in patients with Paget's disease living in the tropics.