ImportanceNew York State’s Medicaid managed long-term care (MLTC) program expanded access to home- and community-based services, providing an alternative to nursing home care for people with dementia. Between 2012 and 2015, the state implemented mandatory MLTC for dual Medicare and Medicaid enrollees requiring more than 120 days of community-based long-term care.ObjectiveTo evaluate changes in nursing home use among older adults with dementia following MLTC implementation.Design, Setting, and ParticipantsThis cohort study used longitudinal data from January 1, 2011, to December 31, 2019, from the Minimum Data Set and Medicare administrative data. The study sample included New York State Medicare beneficiaries 65 years and older with dementia. New York City residents were excluded due to insufficient pre–study period data. Data were analyzed from January 1, 2011, to December 31, 2019.ExposureMandatory MLTC enrollment.Main Outcomes and MeasuresLongitudinal models were used to evaluate changes in annual days of nursing home use following the staggered implementation of MLTC across 13 regions of the state. Two models were estimated: (1) a logistic regression model for any nursing home use in a given year and (2) a linear regression model of total nursing home days, conditional on any nursing home use. Models included annual event-time indicators specified as years until or since MLTC implementation. To capture MLTC effects for dual enrollees relative to non–dual Medicare enrollees, models included interaction terms for dual enrollment and event-time indicators.ResultsThis sample included 463 947 Medicare beneficiaries with dementia who lived in New York State between 2011 and 2019 (50.2% younger than 85 years; 64.4% women). Implementation of MLTC was associated with lower odds of nursing home use among dual enrollees, ranging from 8% lower odds 2 years post implementation (adjusted odds ratio, 0.92 [95% CI, 0.86-0.98]) to 24% lower odds 6 years post implementation (adjusted odds ratio, 0.76 [95% CI, 0.69-0.84]). Compared with a scenario of no MLTC, MLTC implementation was associated with an 8% reduction in annual days of nursing home use between 2013 and 2019 (mean, −5.6 [95% CI, −6.1 to −5.1] days per year).Conclusions and RelevanceThe findings of this cohort study suggest that implementation of mandatory MLTC in New York State was associated with less nursing home use among dual enrollees with dementia and that MLTC may help prevent or delay nursing home placement among older adults with dementia.