We report on four cases of infection by the recently described species Mycobacterium parascrofulaceum. In two cases the mycobacterium was isolated from AIDS patients, while in the others it was responsible for pulmonary disease in elderly men. Our findings suggest that M. parascrofulaceum is an opportunistic pathogen, like many other nontuberculous mycobacterial species. Copyright © 2005, American Society for Microbiology. All Rights Reserved.