AIDS is a chronic, life-threatening disease caused by the human immunodeficiency virus (HIV). HIV attacks the immune system, making people more susceptible to certain types of cancers and infection. Untreated patients generally survive about 10 years. Highly active antiretroviral therapy (HAART), which became widely available in 1996, has significantly reduced illness and death from HIV infection. However, the treatment regimen is expensive and the cumulative costs of treatment are growing as life expectancy increases. A crude estimate of treatment costs for HIV patients in Canada — drugs, physician and hospital visits and lab tests — exceeds $800 million a year. Because this cost estimate is based on simplistic assumptions, health care managers have asked for more accurate tools to help make policy decisions in HIV/AIDS management. Getting a handle on actual costs is particularly important given emerging evidence of an increase in the HIV incidence rate, in BC and across Canada. Karissa Johnston is developing a more sophisticated computer simulation model to accurately estimate the annual and lifetime medical costs for treating people infected with HIV. This tool will also predict how costs will change for various treatment protocols and population groups. Health planners will be able to use these estimates to assess the costs and benefits of disease prevention, drug compliance and various treatment strategies.