This paper provides a review of the legislative reforms and case law that have impacted the defense of Not Criminally Responsible on Account of Mental Disorder (NCRMD) in Canada over the past three decades. As in other jurisdictions internationally, we observe that legislative reforms of procedural, as opposed to substantive, aspects of the NCRMD defense have impacted the manner in which NCRMD criteria are applied in common practice. More people are being declared NCRMD in recent years, and there is greater heterogeneity in the offending and psychiatric profiles of these individuals, suggesting that NCRMD criteria are being applied more liberally over time. In light of the substantial growth of the forensic mental health system over the past two decades, witnessed both in Canada and abroad, we propose that the study of motivational influences underlying the offending behaviors of persons with serious mental illness (SMI) is necessary to begin disentangling symptom‐based offending from violent and antisocial behaviors that may have other motives. This, in turn, can help to determine legal issues, better define the nature of each person's offending and treatment needs, and provide a more fine‐grained analysis of the drivers behind the growth experienced by the forensic system. Copyright © 2013 John Wiley & Sons, Ltd.