Patient registration in a cooperative oncology group refers to the process by which a patient diagnosed at a member institution of the group is entered into the groups records for a selected clinical trial and, where applicable, is issued a random treatment assignment. Patient registration in a cooperative oncology group should not be limited to the routine clerical activities of compiling lists of patients entered on studies and supplying random numbers for treatment assignments. After background material on cooperative oncology groups and statistical issues are presented, the objectives of patient registration are defined to include initiation of data collection, randomization of patients, quality control (enforcing protocol adherence, reduction of bias, suggestion of needed protocol amendments, and evaluation of institutional performance), and planning future clinical trials (providing estimates of patient accrual and providing advice on registration matters). Various administrative procedures found useful in fulfilling these objectives for both randomized and nonrandomized clinical trials that are neither single nor double blind are presented . Foremost among these are the creation of a centralized patient registration staff employing extended telephone registration and a monitoring of patient registration activities through a monthly report system.