Various propositions have been made to improve the statistical quality of medical journals: using statistical referees, promoting better collaboration between statisticians and researchers, and teaching of basic statistics to clinicians. The most frequent errors found in medical articles are misinterpretation of p-values or non-significant results and confusion between statistical and clinical significance, inappropriate use of tests requiring precise assumptions, inappropriate or not controlled multiple testing and particularly testing of post hoc hypotheses, and overemphasis on p-values. Many errors arising from the misinterpretation of results of statistical hypothesis tests, the basic principles of this methodology are emphasized, and the usual fallacies found in the medical literature are reviewed.