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Background: Efficient neuropsychological tests are needed to measure cognitive impairment in moderate to severe dementia. Objective: To examine construct validity of the Severe Impairment Battery Short Version (SIB-S) in nursing home patients with moderate to severe dementia, and to examine potential floor effects for the SIB-S. Methods: Cross-sectional comparison of cognitive measures, dementia severity and functional dependency. Results: A total of 290 patients were included 264 of whom had complete SIB-S protocols. Internal consistency of the SIB-S was very high (Cronbach alpha = 0.97). Principal-component analysis produced three factors, the first of which explained more than 50 % of common scor