Subjective well-being is thought to remain relatively stable into old age despite health-related losses. Age and functional health constraints were examined as predictors of individual differences and intraindividual change in subjective well-being, as indicated by positive and negative affect, using cross-sectional (N = 516) and longitudinal (N = 203) samples from the Berlin Aging Study (age range 70-103 years). In cross-sectional and longitudinal analyses, age and functional health constraints were negatively related to positive affect but unrelated to negative affect. Cross-sectionally, controlling for functional health constraints reversed the direction of the relationship between age and positive affect and produced a negative association between age and negative affect. Findings suggest two qualifications to the average stability of overall subjective well-being: Only some dimensions of subjective well-being remain stable, while others decline; age per se is not a cause of decline in subjective well-being but health constraints are.