This paper analyzes whether education has a protective effect on mental health. To estimate causal effects, we employ an instrumental variable (IV) technique that exploits a reform extending compulsory schooling by one year implemented between 1949 and 1969 in West Germany. We complement analyses on the Mental Component Summary (MCS) score as a generic measure of overall mental health with an MCS-based indicator for risk of developing symptoms of mental health disorder and a continuous measure of subjective well-being. Results support existing evidence of a positive relationship between completed years of secondary schooling and mental health in standard OLS estimations. In contrast, the IV estimations reveal no such causal protective effect and negative effects cannot be ruled out.