This study aimed to introduce clinical manifestations of patients in northeast Iran with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and describe the epidemiological features, as well as risk factors for HTLV-1 infection. This is a cross-sectional study of HTLV-1 infected cases and HAM/TSP patients referred by outpatient neurology clinics as well as Mashhad Blood Transfusion Center from 2005 to 2010. The study comprises 513 cases, including 358 healthy carriers (HCs) and 145 HAM/TSP patients. The majority of carriers were male (73.5%), whereas 67.6% of HAM/TSP sufferers were female (P < 0.001). The mean age of HAM/TSP patients and HCs was 45.9 ± 13.6 and 39.5 ± 11.58 years, respectively (P < 0.001). The history of transfusion, surgery, hospitalization and cupping was observed in a significant greater number of HAM/TSP patients than the HCs (P < 0.001, P < 0.001, P < 0.001 and P = 0.029, respectively). Gait disturbance was the most common complaint in HAM/TSP patients (72.4%). This research develops an HTLV-1 data registry in an endemic area such as Mashhad which can serve useful purposes, including evaluation of clinical and laboratory characteristics of HAM/TSP patients and epidemiological data of HTLV-1-infected cases.