Constitutional chromosome deletions can predispose to the development of cancer with the phenotypic characteristics of inherited cancer syndromes, when the deleted region encompasses a tumour suppressor gene. Examples of such conditions are represented by the cytogenetic deletions associated with retinoblastoma, Wilms tumour and familial adenomatous polyposis. So far, no constitutional deletions involving the genes implicated in hereditary non-polyposis colorectal cancer (HNPCC) have been identified. This may be at least partially because of the lack of distinctive phenotypic manifestations in HNPCC. We describe the first case of a constitutional microdeletion associated with HNPCC. Suspicion of a microdeletion was prompted by the association of mental retardation, postnatal growth deficiency, minor congenital anomalies and early onset (37 years) sporadic colon cancer. The patient was found to harbour a microdeletion within chromosome 2p16-p21, including the MSH2 gene. Since there are very few reports of deletions of the 2p16-p21 region, our observation sets the grounds for the definition of a novel multiple congenital anomaly/mental retardation/cancer microdeletion syndrome.