The aim of this study was to predict retention in residential rehabilitation (RR) services for drug users, focusing on service provider factors. A national postal survey of RR services in England and Wales was carried out and information was obtained from 57 of 87 services identified (65.5%). Service managers were asked to complete a questionnaire asking about treatment philosophy, treatments provided, staff characteristics and staffing levels, as well as overall service size and funding. Services also provided information on the number of clients admitted and the number who had completed, dropped out and been asked to leave in the past year. Completion rates varied widely, from 3% to 92%, with an average of 48%. Higher completion rates were associated with lower counsellor caseloads, fewer beds, single rooms, shorter scheduled treatment durations, higher fees per client and provision of what could be termed a balanced treatment programme containing adequate amounts of individual counselling and programme-free time, and with only moderate demands for domestic duties. Programmes with more drug than alcohol users had lower completion rates, but the proportion of dual diagnosis or criminal justice referred clients did not appear to affect retention. Completion rates varied as a function of a number of service factors that are amenable to manipulation. To retain clients successfully, programmes should not be too large and should have adequate levels of therapeutic staff, a well-developed treatment schedule which is not too demanding for the client in terms of duties or overall time spent in structured activities, and which incorporates sufficient levels of individual counselling. [Meier PS, Best D. Programme factors that influence completion of residential treatment. Drug Alcohol Rev2006;25:349 - 355].