Heavy Trichuris trichiura infestation is rare in developed countries, and complications requiring surgical intervention have been described rarely in human trichuriasis. A case of colonic obstruction and perforation related to heavy whipworm infection is described in an 84 year old woman. The woman was admitted to hospital because of a chest infection. Two days after admission she suffered nausea and vomiting followed a day later by bowel stoppage. Laparotomy indicated intestinal obstruction by a tumour. A partial right sided ileocolectomy was performed. Pathological examination of the resected bowel revealed heavy infestation with T trichiura causing a pseudotumour following a proliferative inflammatory response. (7 Clin Pathol 1997;50:615-616)