Active mycobacterial disease developed in nine of 885 patients undergoing long-term maintenance dialysis during an 81/2-year period. An additional eight patients, who had chronic renal failure but did not require long-term dialysis, contracted active mycobacterial infection during the same interval. Fifty-six percent of the dialyzed group had predominantly extrapulmonary disease and 33% were infected with mycobacteria other than Mycobacterium tuberculosis. Tuberculin sensitivity was present infrequently and examination of sputum and other fluids for acid-fast bacilli was usually unrewarding. The presence of mycobacteria was demonstrated most reliably by tissue biopsy and culture. Failure to diagnose mycobacteriosis resulted in the death of three patients, while the remaining patients responded satisfactorily to drug therapy. © 1980, American Medical Association. All rights reserved.