In a retrospective study of 86 patients with AIDS-defining diseases diagnosed from 1997 to June 2000, i.e. following consolidated and large-scale introduction of highly active antiretroviral therapy (HAART), and 342 control patients diagnosed with AIDS from 1985 to 1995, i.e. the decade preceding the HAART era, the etiological spectrum and the related level of immunodeficiency of each individual AIDS-defining opportunistic infection were compared. The results show that, despite the progress attained in the management of HIV infection since the introduction of HAART, clinicians facing newly diagnosed cases of AIDS will likely encounter a spectrum of opportunistic diseases and a level of underlying immunodeficiency similar to those observed during the decade preceding the introduction of HAART. Even in recent years, the large majority of patients newly diagnosed with AIDS have not been able to take advantage of HAART prior to diagnosis of their disease.