Background: While previous studies have investigated the interplay between affect and health (1) over an extended period of time, (2) in a representative population, and (3) while modelling positive and negative affect simultaneously, no single study has done all three at once. Methods: The present study accomplishes this by sampling adults from the Midlife Development in the US study who completed affect (Mroczek & Kolarz, 1998) and health measures (chronic conditions, Charlson, Szatrowski, Peterson, & Gold, 1994; functional limitations, McHorney, Ware, Lu, & Sherbourne, 1994; self-reported health) measured three times over 20 years. We ran three (one per health metric) random-intercept cross-lagged panel models, where positive and negative affect were modelled simultaneously. Results: Results indicated that positive and negative affect significantly predicted future heath (functional limitations/self-reported health) and that this relationship was reciprocal (i.e. health measures predicted future affect). However, there were no significant cross-lagged relations between affect and chronic conditions. Conclusion: Our results suggest that both positive and negative affect play an equal role in predicting future health for functional limitations and self-reported health as well as highlight the bi-directionality of this relationship. Additionally, the degree to which affect predicts future health may be moderated by the type of health outcome.