This study assessed current practice and methods for improvement in the management of families with hereditary non-polyposis colorectal cancer (HNPCC). HNPCC families registered at five London Genetics Centres and a specialised Colorectal family cancer clinic (CFCC) were identified. Ascertainment of management and outcome details were obtained by scrutiny of patient records and by correspondence with General practitioners (GPs). Two hundred and three families with HNPCC were identified. 79.5% (403/507) of at-risk relatives ascertained were contacted by the genetics centres, and 80.2% (65/81) by the CFCC (P = 1.0). 54.8% (211/385) of probands and relatives within genetics centres' catchment areas were advised to undertake a surveillance programme, compared with 82.1% (64/78) of those cared for by the CFCC (P < 4.2 x 10(-6)). Adherence to surveillance guidelines was 76.6% (49/64) in individuals cared for by the only centre that undertook responsibility for surveillance follow-up (CFCC) and 41.7% (88/211) for the genetics centres, which did not assume responsibility (P < 8.9 x 10(-7)) (using two sided P-values for P (O > or = E/O < or = E)). 15.3% of GPs were unaware their patient had been recommended a surveillance programme, 65% did not know who was responsible for ensuring surveillance follow-up. A questionnaire to fifteen UK genetics centres demonstrated that the majority (86.7%) did not assume responsibility for surveillance follow-up. Since surveillance adherence is clearly better where centres assume responsibility for follow-up, it is recommended that regional or national registers of HNPCC families be developed and maintained to ensure effective management.