New antiretroviral drugs, expanding knowledge of their long-term toxic effects and the large number of patients with treatment failure have increased the demand for new strategies in the antiretroviral treatment of HIV-infected patients. The present study was conducted as part of the HIV Cohort Study in western Denmark to reveal trends in the use of antiretrovirals in the region. The cohort includes all patients attached to those centers treating HIV patients in western Denmark. A total of 537 patients who started highly active antiretroviral therapy (HAART) were included. The number of patients receiving HAART increased dramatically in 1996 and 1997 before leveling off, with 45-75 patients initiating treatment annually thereafter. Median follow-up time after initiation of HAART was 151 weeks. An estimated 45.1% of patients had the initial HAART regimen modified during the first year of follow-up. Side-effects and treatment failure were the main reasons for treatment modifications. Major new strategies implemented in the region in 1999 and 2000 included treatment with boosted protease inhibitors and non-nucleoside reverse transcriptase inhibitors.