The deleterious impact of low mental well-being, and higher levels psychological symptoms (collectively well-being), on concurrent and prospective health outcomes has elsewhere been demonstrated. Further, variables such as conurbation and deprivation have been found to be related to mental and physical heath. This study used data from a longitudinal study to examine which demographic predicted well-being scores, and how scores on these constructs were related to six health-related outcomes. Participants were adolescents (N = 4,956; Male = 2376[48%]), from 72 High Schools in Northern Ireland. Three waves of data were gathered on mental well-being, psychological symptoms, subjective life expectancy (living to age 35 and age 75 years), self-rated health, frequency of physical exercise, and lifetime use of cigarettes and cannabis. Results showed that both well-being scores were significantly associated with gender cross-sectionally, but demographic variables did not predict changes in well-being longitudinally. Both well-being measures were significantly associated with health outcomes cross-sectionally, with mental well-being (over time) predicting life subjective life expectancy, self-rated health, and addictive behaviors, while psychological symptoms (over time) predicted the former two, but not addictive behaviors. Overall, the relationship between mental well-being, psychological symptoms, and the health outcomes assessed, was small in terms of effect size.