To test the feasibility and validity of the Patient Health Questionnaire-9 item interview (PHQ-9) and the newly developed Patient Health Questionnaire Observational Version (PHQ-9 OV) for screening for mood disorder in nursing home populations.The PHQ-9 was tested as part of the national Minimum Data Set 3.0 (MDS 3.0) evaluation study among 3822 residents scheduled for MDS 2.0 assessments. Residents from 71 community nursing homes (NHs) in eight states were randomly included in a feasibility sample (n = 3258) and a validation sample (n = 418). Each resident's ability to communicate determined whether the PHQ-9 interview or the PHQ-9 OV was initially attempted. In the validation sample, trained research nurses administered the instruments. For residents in the validation sample without severe cognitive impairment (3 MS ≥30) agreement between PHQ-9 and the modified Schedule for Affective Disorders and Schizophrenia (m-SADS) was measured with weighted kappas (κ). For residents with severe cognitive impairment (3MS <30), agreement between PHQ-9 interview or PHQ-9 OV and the Cornell Scale for Depression in Dementia (Cornell Scale) was measured using correlation coefficients. Staff impressions were obtained from an anonymous survey mailed to all MDS assessors.The PHQ-9 was completed in 86% of the 3258 residents in the feasibility sample. In the validation sample, the agreement between PHQ-9 and m-SADS was very good (weighted κ = 0.69, 95% CI = 0.61-0.76), whereas agreement between MDS 2.0 and m-SADS was poor (weighted κ = 0.15, 95% CI = 0.06-0.25). Likewise, in residents with severe cognitive impairment, PHQ correlations with the criterion standard Cornell Scale were superior to the MDS 2.0 for both the PHQ-9 (0.63 vs 0.34) and the PHQ-9 OV (0.84 vs 0.28). Eighty-six percent of survey respondents reported that the PHQ-9 provided new insight into residents' mood. The average time for completing the PHQ-9 interview was 4 minutes.Compared with the MDS 2.0 observational items, the PHQ-9 interview had greater agreement with criterion standard diagnostic assessments. For residents who could not complete the interview, the PHQ-9 OV also had greater agreement with a criterion measure for depression than did the MDS 2.0 observational items. Moreover, the majority of NH residents were able to complete the PHQ-9, and most surveyed staff reported improved assessments with the new approach.