The multimodal assessment of capacities in severe dementia (MAC-SD), a novel cognitive and functional assessment, was developed for use with patients with severe dementia. Its psychometric attributes were examined in a unicenter, open, observational study. The MAC-SD along with the Spanish language Severe Mini Mental Exam were administered to 103 patients with a diagnosis of severe dementia. Psychometric analyses were performed to determine acceptability, reliability, validity, and responsiveness. As a whole, the MAC-SD sections showed no floor effects, satisfactory internal consistency, reproducibility, construct validity, precision, and sensitivity to change. The MAC-SD performed as a useful, valid, and potentially responsive tool to measure cognition and functioning in the most advanced stages of dementia.