This paper examines the role of administrative barriers in Medicaid, and how administrative simplification can increase access among eligible beneficiaries. We hypothesize that administrative rules can make applying for and maintaining benefits burdensome, and that this burden will substantially reduce the participation of already eligible beneficiaries. However, has been difficult to test this hypothesis, in part, because estimating the size of an eligible population that is not participating in a program typically requires detailed and accurate survey data. Further, programs rarely change dramatically, and when they do, the effects on participants are not tracked closely. We use high quality administrative data from Wisconsin, combined with a recent expansion and simplification of the state Medicaid program, to identify both the extent to which administrative simplification increases enrollment and who is affected.  Our results show that simplification can be important for increasing enrollment. Moreover, we find that simplification benefits enrollees of a wide range of backgrounds – those who enroll as a result of simplification look very similar to those who had previously enrolled.