In this clinical article, Dr. K K Jain, a neurology consultant in Basel, Switzerland, describes the role of statistics in the practice of medicine and, particularly, in neurology. Most of the applications are in clinical trials. Statistical methods are important for evaluating results of diagnostic tests and epidemiology of disease. They are also important in evaluating results of clinical trials, making diagnoses, and choosing appropriate treatment. Logistic regression can be used for outcome studies and estimation of risk factors as predictors of disease. Bayes’ theorem has been applied to determine if a patent foramen ovale is incidental or causal in patients with cryptic stroke.