This paper discusses medical screening from an economist's perspective. The beneiits and costs of testing are described, including health benefits, direct costs of testing, and labor market impacts. The paper then discusses how workplace characteristics unrelated to worker health can affect the value to employers of medical screening. As a result, employers who maximize the benefits to them of medical screening may reduce the net social benefits of screening. The differences between the private and social benefits of medical screening suggest some areas where medical screening should be used with great care and others that may be the appropriate subjects of regulation.