Although previous research focused on identifying risk factors for mental disorders (or ill-being), recent research has demonstrated a shift towards factors predicting mental well-being. A series of variables from a longitudinal study was used to compare 2 interpretations of mental well-being, namely mental health, defined as lack of DSM caseness, and dispositional optimism. Using logistic and linear regression analyses, the significant predictors of mental health were fewer adverse life events, higher self-esteem, greater perceived social support, and less anticipated depressogenic effects when goals were not met, while optimism was predicted by fewer adverse life events, higher self-esteem, lower neuroticism, and higher femininity scores. After discussion of the implications of both definitions, it is proposed that both can potentially be used as proxies for mental health when more direct well-being measures are unavailable. This article reinforces the need for precise conception(s) of mental well-being, allowing objective measures to guide future research.