This article deals with Occupational Health Surveillance as a health action induced by the workers' knowledge. In order to develop this conception, it adopts the notion of Health Surveillance, especially the concept of problem, and the notion of common-sense knowledge under the perspective used by social psychology. Supported by these considerations, we assume that the formulation of a health problem is a social representation. These considerations are used to examine the practice of "workers' investigations" as conceived by the Italian experience, pointing to its implications for the formulation of problems and identification of strategies in order to act on its determinants.