The present study investigated the rates and perceived effects of past traumatic brain injury (TBI) and substance use in a prison population. Responses to a questionnaire indicated that 86.4% of the 118 respondents had sustained a TBI, with 56.7% reporting more than one, and rates of illicit substance use were higher than the general population. Maori reported 12% more TBI and more substance use than non-Maori. All those with TBI reported difficulties with general memory and socialization on a problem rating scale, but there was no relationship between level of difficulty and severity of TBI, problems with interpersonal relationships, family, and finances were associated with greater substance use.