The aim of this study was to analyze the incidence of new cases, survival of HIV-1-infected patients with progressive multifocal leukoencephalopathy (PML), and the characteristics of PML-associated immune reconstitution inflammatory syndrome (IRIS). Multicenter observational cohort study of all HIV-1-infected patients newly diagnosed of PML in 7 hospitals in Barcelona (Spain) from 2002 to 2006. The annual incidence of PML was calculated. Survival was estimated using the Kaplan-Meier method. IRIS was defined as new onset or rapid worsening of PML shortly after initiation of highly active antiretroviral therapy together with a decline in HIV-1 viral load and rising of CD4 lymphocytes. Sixty-one new cases of PML were diagnosed. The mean survival time was 15 months 95% confidence interval (CI), 11 to 19. The Kaplan-Meier estimates of the probability of survival were 47.7% (95% CI, 35 to 59) at 6 months, 38.6% (95% CI, 25 to 51) at 12 months, 35.1% (95% CI, 22 to 48) at 24 months, and 25.1% (95% CI, 10 to 40) at 36 months. IRIS was diagnosed in 14 (23%) cases. Mortality was similar in patients with and without IRIS. PML continues to be one of the deadliest opportunistic infections in acquired immunodeficiency syndrome patients. The development of PML-associated IRIS has no influence on prognosis.