In March 1999, the Arizona Department of Health Services (ADHS) notified CDC about six cases of gastrointestinal basidiobolomycosis (GIB), an invasive fungal infection. Three cases were reported during January-March 1999, compared with three cases reported during the previous 5 years. This report describes two persons who had representative clinical presentations and summarizes the findings of the investigation of these cases, which indicate that this unusual fungal infection causes severe illness and may be misdiagnosed initially.