The present study was designed to determine the frequency of candidal esophagitis in cancer patients with oral thrush. Patients with clinically and microbiologically diagnosed oral candidiasis were evaluated by endoscopy for concurrent esophageal candidiasis. Esophageal involvement was documented by mucosal lesions, microbiological findings of candidal infection in smears of brushing material, positive cultures of brushing material, and histological evidence of mucosal invasion by the yeast. For 21 of the 22 patients studied, there were endoscopic and microbiological findings of candidal esophagitis. Cultures of the brushing material from all 22 patients were positive, while histological evidence was found for 14 patients. Only 10 of the patients had mild esophageal symptoms. It is concluded that oral thrush represents a reliable marker for esophageal candidiasis in patients with cancer. Routine endoscopy is not necessary to confirm the diagnosis; this procedure should be reserved for patients with persistent thrush and symptoms despite antifungal therapy.