The aim of this cross sectional study was to evaluate bone mineral density (BMD) and serum levels of 25-hydroxy vitamin D (25OHD) in a group of patients taking antiepileptic drugs (AED) for a seizure disorder. Between May-2001 and January-2003, we evaluated 58 patients (40 women/18 men), 34.4+/-6 years old living in Curitiba or in its metropolitan area, on antiepileptic therapy for 2 to 38 years (10 on monotherapy /48 on multiple drugs regime). The group was matched by age, gender, and bone mass index to 29 healthy subjects (20 women/ 9 men); 34.2+/-5.9 years old. Medical history and physical exam were performed on all subjects with particular information sought about fractures and risks factors for osteoporosis. Blood samples were collected for total serum calcium, albumin, phosphorus, creatinine, total alkaline phosphatase, and liver function tests. BMD of the lumbar spine, femur and forearm was determined by dual energy X-ray absorptiometry (DXA, Hologic QDR 1000). Between February and April-2003, other blood samples were collected to measure 25OHD, intact paratohormone (PTH) and calcium. Unemployment and smoking history were more frequent among patients than among controls (p<0.05). Fifteen patients had a fracture history, all of which occurred during a seizure. The BMD of the lumbar spine (0.975+/-0. 13 g/cm2 vs. 1.058+/-0.1 g/cm2; p<0.03) and of the total femur (0.930+/-0.1 g/cm2 vs. 0.988+/-0.12 g/cm2; p<0.02) was lower in patients than in controls. In 63.5% of patients and in 24.1 % of controls a T-score < -1.0 in at least one site was seen. The AED users had higher total alkaline phosphatase and lower 25OHD (p<0.02). No correlations between BMD and 25OHD were found. The use of phenytoin was correlated with a greater incidence of fractures (RR: 2.38). We conclude that patients on chronic use of AED have alterations in bone metabolism characterized in this study by lower BMD of the lumbar spine and total femur and lower serum concentrations of 25OHD.