In the last 10 years, co-infection of human immunodeficiency virus/human T-cell leukemia virus-1 (HIV/HTLV-1) has emerged as a worldwide health problem. These viruses has the same route to infect human but different effects on CD4 positive T-cells. There was controversial results about the influence of coinfection HIV/HTLV-1 pathogenesis. This study compared clinical course and laboratory findings in HIV/HTLV-1 co-infection with HIV mono infection. This historical cohort study carried in Mashhad Consultation Center of Infective and Behavior Diseases, Mashhad, Iran, from April 2013 to March 2017. Persons who referred evaluated by the enzyme-linked immunosorbent assay (ELISA), then patients with positive ELISA test rechecked by ELISA and Western blot. Platelet count, WBC count, neutrophils count, positive CD4 T-cells, staging and disease severity evaluated at diagnosis, in starting and after of antiretroviral therapy in mono and co-infected patients. Demographic characteristics, including age, educational level, occupational state, marriage situation, past medical history and high-risk behaviors were extracted from the files. Of 64 patients enrolled in this study, 61 persons were male. Of 64 participants patients, 42 persons were infected with HIV (35 persons of them were positive for hepatitis C virus), other 22 positive HIV cases, were co infected by HTLV-1 too (18 persons were positive for hepatitis C virus (HCV). Co infected patients had more history of high-risk situations specially intravenous drug abuse. The most common opportunistic infections was cryptogenic tuberculosis (TB), candidiasis and military TB. opportunistic infections and lab findings (except for CD4 positive T-cell) were the same in both group. Clinical severity and disease staging did not differ significantly between two groups. Death was more common in co-infected group. Clinical course in human T-cell leukemia virus-1 (HTLV-1) co-infection has not obvious differences with previously HIV patients compare with only HIV infected patients. In co-infection with the onset of treatment the increase in the level of CD4 positive cells was higher than that HIV infection.