Associations between personality and health may be influenced by contextual factors varying across studied cohorts. Moreover, measurement bias related to contextual factors could also influence these associations. Gender and age have been discussed as important contextual factors when studying personality and health outcomes. An examination of measurement invariance across gender and age may therefore be warranted. In the present study, measurement invariance across age and gender was examined for a five-factor model of personality traits in which scales have been included to operationalise lower-order traits related to health-behaviour or health outcomes. Using multi-group confirmatory factor analysis on a population based cohort (n= 5700), all important parameters of the measurement model were found to be invariant. On the basis of this invariant model, hypotheses of mean differences across age and gender in personality traits were tested. These results were discussed in relation to meta-analyses on personality change and gender differences in personality.