Mucocele of the appendix is a rare lesion, characterised by distension of the lumen due to accumulation of mucoid substance. Mucocele is often asymptomatic and is found incidentally during surgical explorations or ultrasonography studies. This report illustrates the clinicopathologic features of a case of appendiceal mucocele observed during an emergency laparotomy. The surgical treatment consisted in appendicectomy. Colonscopic examination subsequently revealed a left colonic precancerous lesion that was treated with endoscopic polypectomy. The case described underlines the importance of colonic surveillance in patients with mucocele.