We describe 3 HIV-infected patients with disseminated M. genavense infection. The use of corticosteroids possibly favoured colonization and dissemination of atypical mycobacteria in these patients with low CD4 cell counts and may have masked symptoms of infection. The fact that these patients were treated with highly active antiretroviral therapy (HAART) together with antimycobacterial therapy may explain that 1 patient was free from mycobacteria 16 months after the end of specific treatment. Hospital tap water contained M. genavense at a concentration of >10 bacteria/l as examined by PCR. This species caused 12% of cases of non-tuberculous disseminated mycobacteriosis in HIV-infected patients at our hospital.