Abstract Twenty patients with gastrointestinal mucormycosis are reviewed. This often fatal opportunistic fungal infection was diagnosed histologically, and was categorized as colonization (five patients), infiltration (seven patients), or vascular invasion (eight patients). There were no fatalities from colonization. In 10 patients, mucormycosis complicated peptic ulcer disease. Seven of these patients had infiltrative or invasive disease. The presentation and operative findings mimicked malignancy in five of these seven patients, and six had successful surgical intervention. The other patient was cured by medical therapy alone. Ten patients had infection associated with other gastrointestinal diseases: post-traumatic peritonitis (four patients), transmural amoebiasis (two patients), tuberculosis (one patient), gastroenteritis (one patient), gastric carcinoma (one patient) and diabetes (one patient). Eight patients had significant infection and only one survived. In this series, mucormycosis had a less aggressive course when complicating peptic ulcer than when it occurred in association with other gut diseases.