Social health insurance reform has evolved as an important public policy issue in several European countries. Some of the most important reform programs have been the introduction of managed competition, a shift from full retrospective reimbursement of health insurers to prospective reimbursement,an increase of private payments, and a change in the health benefits of social health insurance. The article investigates the widespread assumption that reform programs have adverse effects on solidarity in social health insurance by looking at the concrete experience of four European countries (Belgium,Germany, the Netherlands, and Switzerland) over the past decade. A distinction is made between risk solidarity and income solidarity, and the scope of solidarity is shown to have two dimensions: entitlements and membership. The analysis consists of three parts: description of the structure of health insurance of each of the four countries in the early 1990s; discussion of health insurance reform; determination of the impact on each dimension of solidarity. The findings are mixed. There are indeed some examples of solidarity having declined as the result of health insurance reform. But, more important, many examples also were found of an increase in solidarity due to health insurance reform. In some cases, reform was explicitly intended to improve solidarity. If a reform program had a negative impact on solidarity(e.g., an increase in private payments), accompanying measures often were taken to keep solidarity intact as much as possible. Thus the assumption of a negative impact as a result of health insurance reform is not confirmed.