Background There is evidence that people with mental disorders are at increased risk of victimisation in prison. It is unclear whether this risk of victimisation varies across types of disorders or symptoms and what role mental health treatment has on victimisation risk in this context. Aims To examine the relationship between specific mental disorders, psychiatric symptoms, and victimisation in prison and the effect of treatment for the disorders on victimisation risk. Methods Using a nationally‐representative sample of prisoners, path analyses were conducted to examine the relationship between mental disorder and victimisation. The analyses also examined whether receiving mental health treatment in prison affected any such relationship. Results Victimisation risk varied with the type of mental disorder or symptoms. Depression, personality disorder, hopelessness, paranoia, and hallucinations were associated with increased victimisation risk. Psychotic illnesses were otherwise negatively associated with victimisation. Receiving mental health treatment in prison was associated with greater risk of victimisation there. Receiving treatment appeared to mediate the relationship between mental disorders, symptoms, and victimisation. Conclusions The findings suggest that not all inmates with mental disorders are at an increased risk of victimisation. Further, mental health treatment in prison also appears to be a risk factor of victimisation. More research is needed to further elucidate the relationship between mental disorders, treatment, and victimisation. Copyright © 2017 John Wiley & Sons, Ltd.