We explore alternative measures of unobserved health status in order to identify effects of mental and physical capacity for work on older men's retirement. Traditional self-ratings of poor health are tested against more objectively measured instruments. Using the Health and Retirement Study (HRS), we find that health problems influence retirement plans more strongly than do economic variables. Specifically, men in poor overall health expected to retire one to two years earlier, an effect that persists after correcting for potential endogeneity of self-rated health problems. The effects of detailed health problems are also examined in depth.