<p>This study (1) developed the Japanese version of the Inventory of Statements About Self-injury (ISAS), a tool for assessing the functions of nonsuicidal self-injury (NSSI), and (2) classified NSSI in adolescents based on its functions. We administered a questionnaire to a community sample and gathered 592 responses, including those of 267 undergraduates who had experienced NSSI. The results of factor analysis indicated that the Japanese version of the ISAS was different from the original and was composed of three factors: "Distress coping functions," "Interpersonal influence functions," and "Identity maintenance functions." Cluster analysis of the Japanese version of the ISAS scores indicated four clusters: "Habitual cluster," "Distress coping cluster," "Overlapped identity maintenance cluster," and "Overlapped interpersonal influence cluster." Each cluster's clinical features indicated that the more the functions overlapped, the more severe were risks of suicide, anxiety, and depression. These results indicated that the significance of NSSI functions' assessment was related to their overlap. These results suggested the usefulness of the functional approach to treatment.</p>