This study examines the health consequences of social disconnectedness and perceived isolation among older adults, using data from the National Social Life, Health, and Aging Project (NSHAP). Social disconnectedness is defined by a lack of social relationships and low participation in social activities, while perceived isolation is characterized by feelings of loneliness and a perceived lack of social support. The research combines multiple indicators of social isolation into scales assessing these two forms of isolation. The findings indicate that both social disconnectedness and perceived isolation are independently associated with lower self-rated physical health. However, the relationship between social disconnectedness and mental health may be mediated by perceived isolation, as the association between social disconnectedness and mental health weakens when perceived isolation is controlled for. The study concludes that health researchers need to consider both social disconnectedness and perceived isolation simultaneously to fully understand their health impacts.This study examines the health consequences of social disconnectedness and perceived isolation among older adults, using data from the National Social Life, Health, and Aging Project (NSHAP). Social disconnectedness is defined by a lack of social relationships and low participation in social activities, while perceived isolation is characterized by feelings of loneliness and a perceived lack of social support. The research combines multiple indicators of social isolation into scales assessing these two forms of isolation. The findings indicate that both social disconnectedness and perceived isolation are independently associated with lower self-rated physical health. However, the relationship between social disconnectedness and mental health may be mediated by perceived isolation, as the association between social disconnectedness and mental health weakens when perceived isolation is controlled for. The study concludes that health researchers need to consider both social disconnectedness and perceived isolation simultaneously to fully understand their health impacts.