Background: Access with evidence development has been established for expensive intramural drugs in The Netherlands. The procedure involves a 4-year period of conditional reimbursement. During this period, additional evidence has to be gathered usually through a patient registry. Given the costs and time involved in gathering the data, it is important to carefully evaluate the registry. Objectives: This study aimed to develop a model for the regular evaluation of patient registries during an access with evidence development process and find the optimal length of the registry period. Methods: We used data from a recent registry in The Netherlands on oxaliplatin as a treatment option for stage III colon cancer. We added simulated follow-up data to the empirical data available and applied value of information analysis to balance the gains of extending the period and amount of data gathering against the costs of registering patients. Results: We show that given the assumptions on cohort size, follow-up time, and purpose of the registry, the current (partly simulated) registry was not very efficient. Notably, the observation period could have been stopped to make a definite reimbursement decision after a maximum of 2 years rather than the fixed 4-year period. Conclusions: Patient registries may be an efficient way to gather data on new medical treatments, but they need to be carefully designed and evaluated, in particular regarding their follow-up time. For each purpose, data gathering can be tailored to make sure decisions are taken at the moment that sufficient data are available. Copyright (C) 2015, International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc.