Therapeutic use of marijuana has emerged as an important issue for people living with cancer, HIV/AIDS and multiple sclerosis. This paper examines therapeutic use of marijuana in the Positive Health cohort study, a longitudinal cohort study of men and women living with HIV/AIDS in NSW and Victoria, Australia. Factors that distinguish therapeutic use of marijuana from recreational use were assessed by comparisons on a range of social and health-related variables. The results show that among 408 participants, 59.8% reported some use of marijuana in the past six months. Of those participants (n=244), 55.7% reported recreational use only of marijuana and 44.3% report mixed use of marijuana for therapeutic and recreational purposes. Multivariate logistic regression analysis showed that participants who used marijuana for therapeutic purposes were significantly more likely than recreational-only users to have used other complementary or alternative therapies, experienced HIV/AIDS-related illness or other illnesses in the past 12 months, had higher CD4/T-cell counts, had lower incomes, be younger in age and less likely to have had a casual partner in the six months prior to interview. These results show that a substantial proportion of people living with HIV/AIDS (PLWHA) use marijuana for therapeutic purposes, despite considerable legal barriers, suggesting marijuana represents another option in their health management. Rather than solely using marijuana in response to illness, the experience of illness may influence a person's understanding of their marijuana use, so that they come to understand it as therapeutic. Further research might consider possible interactions between cannabinoids and antiretroviral treatments, potential use of oral THC and the difficulties faced by clinicians and PLWHA in discussing marijuana in the current legal context.