An 81-year-old woman had abdominal cramps, rectal bleeding since 2 weeks and weight loss. Colonoscopy showed an ulcerating tumour of about 4 cm in the transverse colon. Pathological examination of biopsies taken during colonoscopy indicated moderately active chronic colitis. Based on the colonoscopy findings, the tumour appeared to be malignant and laparotomy was performed and the transverse colon was resected. Pathological examination of the resected lesion revealed a submucosal lipoma. The patient recovered fully. Lipomas account for 4% of benign gastrointestinal tumours and 90% of lipomas are submucosal. Their presentation is often similar to malignant tumours. The naked fat sign after biopsy and the elasticity of the lesion are typical features encountered during colonoscopy. Given the high fat content of these lesions, they are easily discernible with CT and MRI. Lipomas with a diameter < 2 cm can be safely removed endoscopically. Larger lesions should be removed by segment resection.