Objectives: To validate the Psychogeriatric Inventory of Disconcerting Symptoms and Syndromes (PGI-DSS), a single scale in A4 format comprising four disconcerting syndromes (violence, refusal, words, and acts). The scale enables an immediate conversion of a qualitative assessment to a quantitative assessment. The PGI-DSS was compared with the Neuro Psychiatric Inventory for Nursing Homes (NPI-NH). Design: Cross-sectional descriptive and correlational studies. Setting: Thirty geriatric care units and nursing homes. Participants: Raters interviewed nurses and nursing assistants in charge of older adults hospitalized in geriatric care units or living in nursing homes (N = 226). Measurements: The French version of the PGI-DSS and the French version of the NPI-NH. Results: The correlation coefficient between the PGI-DSS and the NPI-NH was 0.70 (p < 0.0001). The PGI-DSS threshold score corresponding to the NPI threshold score was 17 (specificity: 87%, sensitivity: 63%). Four statistical factors, corresponding to the four clinical syndromes, explained 53.4% of the total variance. The internal consistency of the PGI-DSS (Cronbach's alpha = 0.695) was higher than that of the NPI-NH (Cronbach's alpha = 0.474). Test-retest reliability was better for the PGI-DSS than for the NPI-NH. The intraclass correlations were 0.80 [0.73; 0.86] and 0.75 [0.67; 0.83], respectively. Interrater reliability was better for the PGI-DSS than for the NPI-NH. The intraclass correlations were 0.65 [0.55-0.76] and 0.55 [0.43-0.68], respectively. Conclusion: The PGI-DSS was developed to overcome the limitations of the NPI-NH. New, brief, easy to administer in less than 4 minutes, foldable in four parts, pocket-sized, easy-to-read in the palm of the hand, PGI-DSS could have similar or better statistical properties than the NPI-NH. Whereas the 10 domains in the NPI-NH have clinical utility for clinicians, the four easily understandable syndromes in the PGI-DSS can help avoid inappropriate attitudes and can guide psychosocial interventions. It could likewise improve dialogue between caregivers and clinicians.