Objective: To examine the relationship of social isolation, loneliness and health outcomes among older adults. Methods: Using data from the Leave Behind Questionnaire of the Health and Retirement Study (2006 and 2008), (n = 11,825) several indicators of social isolation were scaled and the Hughes 3-Item Loneliness Scale was used. Two measures of health (self-rated health and mental health conditions) were examined using logistic regression. Results: Loneliness and social isolation were not highly correlated with one another (r = 0.201, p = 0.000). Loneliness was associated with higher odds of having a mental health problem (OR: 1.17; CI: [1.13, 1.21], p = 0.000); and isolation was associated with higher odds of reporting one’s health as being fair/poor (OR:1.39; CI: [1.21, 1.59], p = 0.000). Discussion: The results suggest that global measures of isolation, that fail to distinguish between social isolation and feelings of loneliness, may not detect the impact on physical and mental health in older adults.