Research suggesting nonsuicidal self-injury (NSSI) may belong in a distinct diagnostic category has led to the inclusion of NSSI disorder in the DSM–5 section for future study. There has been limited research, however, examining the validity of Criterion A (the frequency criterion). The current study aimed to examine the validity of the frequency criterion of NSSI disorder through the use of an exploratory data mining method, structural equation modeling trees, as a way to determine a NSSI frequency that optimally discriminates pathological NSSI from normative behavior among undergraduate students (n = 3,559), 428 who engaged in NSSI in the previous year. The model included psychopathology symptomology found to be comorbid with NSSI and cognitive-affective deficits commonly associated with NSSI. Results demonstrated a first split between individuals with 0 and 1 act of NSSI in the past year, as was expected. Among individuals with 1 or more previous acts, the optimal split was between those with 5 and 6 NSSI acts in the past year. Results from the current study suggest that individuals with 6 acts of NSSI in past year, compared with those with 5 acts or less, may represent a more severe group of self-injurers. These individuals reported higher levels of related psychopathology symptomology and cognitive-affective deficits, in addition to decreased quality of life. Findings have potential implications for the proposed frequency criteria of NSSI disorder and how pathological NSSI is characterized.