Epidemiological studies, more specifically those related to analytical epidemiology are a major determinant of evidence-based medicine. When classifying the value of the different epidemiological studies, based on their level of causality, cohort studies are ranked higher than case-control studies, mainly due to the fact that they allow direct collection of information on exposition to risk factors and health consequences. However, case-control studies can also provide an important information, if a specific effort is dedicated to the analyses of the circumstances of the exposition. Meta-analysis increases, by pooling them, the statistical power of individual studies of limited size. Meta-analysis can also be considered as an important source of evidence in the perspective of evidence-based medicine.