Summary Evidence based practice has become a golden standard in modern medicine. Before searching for evidence, a clinical question including the population in focus, the intervention and maybe control treatment and the relevant outcomes must be posed. Hereafter a comprehensive search will yield the published evidence to enlighten the question. The papers must be critically evaluated and bias assessed. Published material will tend to overestimate the treatment effect because of publication bias, language bias, the fact the authors and journals strive for significance instead of true results and the fact that for many interventions the evidence is low quality trials. Methods and challenges are discussed.