Diabetic patients are at risk of acquiring esophageal infections such as those caused by members of the genus Candida. Here we describe a case in which Candida guilliermondii was isolated from the esophageal mucosa of a patient with uncontrolled diabetes mellitus. Due to inappropriate and inaccurate identification, the emergence of non-C. albicans Candida species as potential pathogens has been underestimated. This should be a cause of concern since C. guilliermondii is a normal component of human microbiota. The identity of the isolate in our case was confirmed by its characteristic morphophysiological features and amplification of rDNA using species-specific primers. Fluconazole therapy produced no improvement of the esophageal symptoms, and resistance of the etiologic agent was confirmed through in vitro susceptibility tests. This is thought to be the first documented case of C. guilliermondii esophagitis in a patient with diabetes mellitus.