Objective: To determine the psychometric properties of the Montreal Cognitive Assessment (MoCA) in patients with a learning disability and examine it's utility for conducting mental capacity assessment. Method: This study was a cross-sectional, instrument validation study in an inpatient hospital setting, located in the East of England. The sample consisted of two groups: (i) 31 consecutively admitted hospital patients and (ii) 10 multidisciplinary team members who served as a comparison group. The MoCA, a 12-item screen for mild cognitive impairment and the Dysexecutive Questionnaire (DEX), were used in this study. Item analysis was conducted by comparing item endorsement for all participants that had a learning disability utilising Difficulty and Discrimination Indices for each item on the MoCA. We examined the internal consistency of a revised scale derived from item analysis and used a one-way ANOVA to determine concurrent validity by comparing scores between two patient subgroups and the comparison group. Results: A 7-item scale, "MoCA-LD" (alpha coefficient = 0.82) emerged from item analysis. A statistically significant negative correlation was observed between MoCA-LD and DEX (Pearson correlation = -0.66, P < 0.01). As expected, participants in the borderline category scored higher on MoCA-LD than those with mild learning disability, as did those with no learning disability (P < 0.001). Conclusion: The MoCA-LD has the potential to be a useful tool for mental capacity assessment in patients with a learning disability.