The study aimed to identify the relationships between patterns of non-suicidal self-injury (NSSI), their severity, and suicide attempts among 107 youth (aged 15–25 years) with borderline personality disorder (BPD). Two principal patterns were identified via a graphical representation of retrospectively reported 12-month histories of NSSI. These were habitual (NSSI occurring at regular intervals) and random patterns (NSSI inconsistently spaced). Habitual patterns of NSSI were associated with lower severity and fewer suicide attempts than random patterns. Within-person comparisons revealed a reduction in NSSI engaged within a habitual pattern and an increase in NSSI engaged within a random pattern in the month prior to a suicide attempt. Findings suggest that the accuracy of risk assessments among youth with BPD might be improved by identifying an individual’s historical pattern of NSSI, as well as any relative increase in NSSI engaged within a random pattern or relative reduction in NSSI engaged within a habitual pattern.