While the detrimental health effects of self-perceived job insecurity are well documented, less is known about the mechanisms through which insecurity affects health. In this article, potential explanations for this relationship are examined separately for three age groups (18–35, 36–50, and 51–65). Mediation analyses based on the German Socio-economic Panel show an ‘immediate shock effect’ that occurs when a person becomes worried, as well as a ‘prolonged stress effect’ that sets in when job loss worries persist over a longer period. Second, the results reveal that for middle-aged workers, both effects of self-perceived job insecurity are largely explained by the following factors: perceived financial problems, feelings of stress, exhaustion, and anxiety, a perceived lack of control, and family dissatisfaction. Yet it appears that these factors do not fully explain the detrimental health effects of job insecurity among younger or older workers.