The article by Marcel E. Salive examines the prevalence and impact of multimorbidity, the coexistence of two or more chronic conditions, among older adults. Using population-based administrative claims data from nearly 31 million Medicare beneficiaries, the study found that 67% had multimorbidity, which increased with age, from 50% for those under 65 to 81.5% for those 85 and older. A systematic review of 16 other studies confirmed the high prevalence of multimorbidity, with a median prevalence of 63% and a mode of 67%. The article highlights methodological issues in defining multimorbidity, including the type and number of chronic conditions included, ascertainment methods, and source populations. Standardized methods are needed for public health surveillance and prevention. Multimorbidity is associated with increased risk of death, disability, poor functional status, poor quality of life, and adverse drug events. The article calls for more research to understand causal pathways and develop clinical and population interventions targeting multimorbidity.The article by Marcel E. Salive examines the prevalence and impact of multimorbidity, the coexistence of two or more chronic conditions, among older adults. Using population-based administrative claims data from nearly 31 million Medicare beneficiaries, the study found that 67% had multimorbidity, which increased with age, from 50% for those under 65 to 81.5% for those 85 and older. A systematic review of 16 other studies confirmed the high prevalence of multimorbidity, with a median prevalence of 63% and a mode of 67%. The article highlights methodological issues in defining multimorbidity, including the type and number of chronic conditions included, ascertainment methods, and source populations. Standardized methods are needed for public health surveillance and prevention. Multimorbidity is associated with increased risk of death, disability, poor functional status, poor quality of life, and adverse drug events. The article calls for more research to understand causal pathways and develop clinical and population interventions targeting multimorbidity.