The first 2 cases of infection with Enterocytozoon bieneusi in Denmark and Scandinavia are reported. Both patients were women and to the best of our knowledge this is the first report of E. bieneusi in female AIDS patients. Both had late stage AIDS, and both had complained of intermittent diarrhoea for more than 1 year. At the time microsporidiosis was diagnosed, no other pathogens causing diarrhoea were found. Immunodeficient patients with chronic unexplained diarrhoea should be investigated for intestinal microsporidiosis, especially as treatment is now available.