Between 1980 and 1989, the Public Health Laboratory Service Regional Tuberculosis Centre, Dulwich, received cultures of mycobacteria isolated from urine and the genitourinary tract of 1392 new patients: 803 isolates were members of the tuberculosis complex (753 M. tuberculosis, 45 M. bovis, 4 M. africanum) and 589 were various species of environmental mycobacteria. The incidence of the latter isolations varied by region and by year and, with 17 exceptions (13 from endometrial curettings, 2 from hydrocele fluid, 1 from a scrotal abscess and 1 from a kidney), all isolations of environmental mycobacteria were from urine; very few of them appeared to be clinically significant. Those that could be significant included 1 isolate from a kidney, 1 from a post-renal transplant patient and 4 from patients with AIDS, 3 of whom had disseminated mycobacterial disease. Reports of clinically significant isolations of environmental mycobacteria from the genitourinary tract are reviewed.