To evaluate the mechanism and risk factors associated with the nosocomial acquisition of Candida albicans, a 10-month prospective study was conducted in a 24-bed bone marrow transplant unit and an 8-bed medical intensive care unit of a university hospital. A total of 98 patients had samples taken on admission and during hospitalization for culture. Samples from hands of hospital personnel and environmental surfaces were also cultured. C. albicans was isolated from 52 patients, and each patient was matched with a control. Fourteen patients acquired C. albicans after admission to the study. Prior antibiotics and length of time spent in the unit were more common in patients with new acquisition of C. albicans than in controls (92% vs. 64% and 32.5 vs. 13.0 days, respectively). Restriction enzyme analysis revealed 32 strain types; 4 were common to 30 patients and 10 environmental surfaces. Identical strains of C. albicans from patients who were geographically and temporally associated suggests the exogenous nosocomial acquisition of C. albicans through indirect patient contact.