The purposes of this study were to review investigations on 'Tojikomori' elderly in Japan, and to examine valid definitions of 'Tojikomori' as a risk factor for functional decline. In the present study, we reviewed 94 studies in the literature. 86 obtained from Japan Centra Revuo Medicina, version 3 (systematic literature search system for Japanese literature). We added 8 studies from references in 86 reports in the literature. The number of publications on 'Tojikomori' has rapidly increased since 2000. In the existing literature, 'Tojikomori' has been defined using one or more of the following four elements; (1) Extent of daily activity, (2) Frequency of going out, (3) Frequency of contact with others, and (4) Mobility. The definition using "Frequency of going out" has gained favor in recent years. This study reviewed three papers that examined the validity of the 'Tojikomori' definition as a risk factor for functional decline. Future study is required with attention to the following three points: (1) larger sample size and longer follow-up: (2) plural definitions: and (3) control for confounding factors.