Objective. To examine the impact of using highly active antiretroviral therapy (HAART) in a human immunodeficiency virus (HIV) infected population on the chemotherapy related costs of treating acquired immunodeficiency (AIDS)-related cancers. Methods. We used the Southern Alberta Clinic (SAC) database to define the incidence and prevalence of AIDS-related cancers in a geographically defined HIV population in both the pre- HAART and HAART eras, and subsequently, the Alberta Cancer Board Pharmacy database to determine the chemotherapy associated costs of the cancer treatment. Results. During both eras, 60% of AIDS-related cancer patients received chemotherapy. The absolute number of patients treated in the pre-HAART era was 70, but during the HAART era, due to the decreased incidence of these cancers, only 13 patients received chemotherapy. The number of distinct regimens used for AIDS cancer treatment standardised, and decreased from 29 to six between eras. The average per patient cost of chemotherapy in the pre-HAART era was $6111, while in the HAART era it rose to $8817. However, the cost avoidance in chemotherapy costs, due to HAART use in the ‘at risk’ population, averaged $123 439/year or $471 per ‘at risk’ patient. Conclusion. The introduction of HAART has dramatically reduced the amount spent on chemotherapy due to a decreased incidence of AIDSrelated cancers, even though the individual patient treatments have become more effective and expensive. J Oncol Pharm Practice (2007) 13: 17-25.