Familial adenomatous polyposis (FAP) is a multi-system disease characterised by the development of hundreds to thousands of colorectal adenomas which inevitably progress to carcinoma without treatment. It is commonly associated with extra colonic lesions including osteomas, epidermoid cysts and desmoid tumours. Desmoid tumours are troublesome due to their size and bulk and are a significant cause of morbidity and mortality in FAP. This series highlights three cases in which patients with FAP developed masses thought initially to be manifestations of the condition. Further investigation in fact demonstrated neurofibromatosis type 1 in all three patients. All masses in FAP patients cannot be assumed to be disease related (desmoid, osteoma, epidermoid cyst or carcinoma).