This study unites two perspectives concerning the determinants of job insecurity perceptions that exist in the literature and that resemble the classical nature–nurture debate. On the ‘nurture’ side, we investigated the company performance and type of contract, while we focused on negative affectivity and locus of control on the ‘nature’ side. In addition to demonstrating the known main effects of the respective predictors, we examined the proportional reduction in prediction error for both predictor types. Based on Lazarus’ stress model, we also hypothesized interactive effects between the environmental and person-related predictors. Multilevel analyses of 640 employees from 50 companies revealed that all four variables significantly and incrementally predicted job insecurity in the hypothesized direction. Interestingly, the person-related variables contributed more than twice as much to the reduction in prediction error in job insecurity perceptions when compared with the environmental variables. Among the hypothesized interaction effects, only locus of control significantly interacted with type of contract in predicting job insecurity perceptions (employees on a temporary contract experienced a steeper incline in job insecurity perceptions with increasing levels of external locus of control relative to employees on a permanent contract). We discuss implications for the conceptualization of job insecurity as well as practical implications.