The Oregon Health Plan (OHP), Oregon's section 1115 Medicaid waiver program, expanded eligibility to all residents living below poverty. We use survey data, as well as OHP administrative data, to profile the expansion population and to provide lessons for other States considering such programs. OHP's eligibility expansion has proved a successful vehicle for covering large numbers of uninsured adults, although most beneficiaries enroll for only a brief period of time. The expansion population, particularly childless adults, is relatively sick and has high service use rates. Beneficiaries are also likely to enroll when they are in need of care.