Case-crossover study is research using only data from cases, patient with interested event. Getting control from own data, the case-crossover study is classified into self-controlled study. It has a lot of condition to be valid study. When study satisfies the conditions, the case-crossover has a lot of advantage in which it is not necessary to collect information of control group patients, and the control is to be matched genetic and other background. The paper is summarized the case-crossover study design. (Jpn J Pharmacoepidemiol 2013; 18(2): 90-94)