Cryptosporidium is a coccidial protozoan of the intestinal tract; cryptosporidiosis in veterinarians has been reported as a cause of diarrhea. It has also been reported as a cause of diarrhea in marrow transplant recipients. Cryptosporidiosis has gained attention recently because of its occurrence in patients with the acquired immune deficiency syndrome (AIDS). A healthy intensive care unit nurse who acquired cryptosporidiosis from a bone marrow transplant recipient with diarrhea caused by cryptosporidiosis is described. Results of laboratory examination, including T lymphocyte subsets, were normal. She was treated with bed rest and a liquid diet and her symptoms completely resolved after 15 days. Health care workers should be aware that cryptosporidiosis can be transmitted to them from patients and should follow precautions to avoid acquiring the disease.