The authors analyse the difficulties of the knowledge given by epidemiological studies from the clinician's point of view. They propose three arguments to define the aid epidemiology can bring to clinicians: to give rise to hypotheses from clinical experience, validate some epidemiological results, and reflect on the integration of predictive knowledge in clinical practice. These arguments are illustrated by examples taken from the authors work and propositions of epidemiological studies of which the aim and the problematic could emanate from observation and clinical experiences.