OBJECTIVE: The aim of the study was to determine rates of utilization of in-patient, out-patient and laboratory services stratified by virological and immunological markers of HIV disease among patients on antiretroviral treatment in British Columbia, Canada. METHODS: We estimated resource utilization for in-patient visits, out-patient visits, and laboratory tests among patients initiating antiretroviral treatment between 1 April 1994 and 31 December 2000, with follow-up to 31 March 2001. Resource use was stratified by CD4 cell count and plasma HIV viral load (pVL) at the time of utilization and rates per 100 patient-years were calculated for each health care resource. RESULTS: A total of 2718 patients were included in our analyses. The overall rates of in-patient visits, out-patient visits, and laboratory tests were 902, 3001 and 840 per 100 patient-years, respectively. Utilization was higher for patients with low CD4 cell counts and high pVLs when compared with patients with high CD4 cell counts and low pVLs. CONCLUSIONS: Patients with low CD4 cell counts and high pVLs had the highest use of health care services. Regular follow-up with health care providers in an out-patient setting, allowing for proper monitoring and maintenance of HIV care, is important in minimizing unnecessary and potentially costly in-patient care.