Background: Little is known about the socio-demographic, clinical and legal determinants of mental health court decisions of unsoundness of mind and unfitness to stand trial for people with cognitive disability. We aimed to estimate the association between severity of cognitive disability and mental health court determinations of unsoundness or unfitness and describe the socio-demographic, clinical and legal factors that predict these determinations. Methods: Case file data were extracted on 92 individuals who had a criminal case referred to the Queensland Mental Health Court between 1 January 2013 and 31 December 2014 due to cognitive disability. We fit a modified multivariable Poisson regression model to estimate the association between severity of cognitive impairment and mental health court determination, controlling for socio-demographic, clinical and legal factors. Results: Adjusting for covariate effects, severity of cognitive impairment was positively associated with being found unfit to stand trial (adjusted prevalence risk ratio = 1.57; 95% confidence interval: 1.07, 2.33; P = 0.023), and comorbid psychotic disorder predicted an increased risk of being found unsound of mind at the time of offence (adjusted prevalence risk ratio = 3.63; 95% confidence interval: 1.38, 9.54; P = 0.009) by the Queensland Mental Health Court. Conclusions: Severity of cognitive disability is associated with determinations of unfitness but does not predict determinations of unsoundness in the Queensland Mental Health Court. Psychiatric assessments of cognitive impairment play a pivotal role in mental health court determinations for people with cognitive disability.