HIV-associated multicentric Castleman disease (MCD) is associated with a high risk of developing non-Hodgkin lymphoma (NHL). Rituximab is effective in HIV-MCD, but its impact on NHL incidence remains unknown. From a single-center prospective cohort, 113 patients were identified with a diagnosis of HIV-MCD for the present study. To compare the incidence of NHL between patients who had received a rituximab-based treatment (R+ group) and those who had not (R- group), data were analyzed before and after matching on propensity scores and after multiple imputation. The mean follow-up was 4.2 years. In the R- group (n = 65), 17 patients developed NHL (incidence, 69.6 of 1000 person years). In the R+ group (n = 48), only 1 patient developed NHL (incidence, 4.2 of 1000 person years). Based on the propensity score-matching method, a significant decrease in the incidence of NHL was observed in patients who had been treated with rituximab (hazard ratio, 0.09; 95% confidence interval, 0.01-0.70). Ten Kaposi sarcoma (KS) exacerbations and 1 newly diagnosed KS were observed in 9 patients after rituximab therapy. Rituximab was associated with an 11-fold lower risk of developing lymphoma. KS exacerbation was the most challenging adverse event after rituximab therapy.