Human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) has been associated with changes in extracellular matrix of neural tissue. HTLV-I infection has multiple other systemic effects. Extracellular matrix is important for bone mineral deposition. We examined bone mineral density (BMD) in patients with HAM/TSP. BMD was assessed by ultrasonographic calcaneous densitometry in 24 patients (7 males, 17 females) with HAM/TPS, and 23 healthy HTLV-I-seronegative controls matched by age and sex. Patients with HAM/TPS had a mean BMD T-score of -3.07 +/- 0.64 in males and -2.93 +/- 0.69 in females. Control patients revealed a T-score of -0.77 +/- 1.31 in males and -1.17 +/- 1.08 females. The difference in T-score between HAM/TSP patients and control groups is significant (P < 0.001). Of HAM/TPS patients, 7 of 24 (29.2%) had osteopenia (T-score between -1 and -2.5) and 17 of 24 (70.8%) were diagnosed with osteoporosis (T < -2.5). Respective figures for control patients were 10 of 23 (43.5%) with a normal T-score, 11 of 23 (47.8%) with osteopenia, and 2 of 23 (8.7%) with osteoporosis. After adjustment for age and sex, odds ratio of osteoporosis for HAM/TSP patients was 31.52 (95% confidence interval, 5.07 to 195.88). No correlation was found in HAM/TSP patients between T-score and age, menstrual status, gait functionality, or years of evolution of HAM/TSP. HAM/TSP patients have a significantly diminished BMD of the calcaneous that appears not to be explained by paresis, age, years of disease, menstrual status; may be the result of systemic alterations due to HTLV-1 infection.