Resumen: Prior studies have identified a positive effect of an individual’s educational attainment on their mental well-being. However, this effect appears to be less pronounced among university graduates. Two potential explanations for this phenomenon are overeducation and the possible existence of reverse causality. The aim of this study is to examine the relationship between overeducation and indicators of poor mental health, among highly educated workers in Spain, considering the possible mutual influence between these variables. To this end, the Simulated Maximum Likelihood method is employed to control potential simultaneity effects, using data from the last two waves (2014, 2020) of the European Health Interview Survey. The results obtained suggest that, among highly educated workers, overeducation does not appear to result in a decline in mental health. Conversely, they indicate that mental conditions may play a role in the phenomenon of overeducation in the workplace. Different arguments are posited as potential explanations for the outcomes observed. Idioma: Inglés DOI: 10.1007/s11205-025-03690-y Año: 2025 Publicado en: Social Indicators Research (2025), [20 pp.] ISSN: 0303-8300 Financiación: info:eu-repo/grantAgreement/ES/AEI/PID2020-118355RB-I00 Financiación: info:eu-repo/grantAgreement/ES/DGA/S32-23R Tipo y forma: Article (Published version) Área (Departamento): Área Fund. Análisis Económico (Dpto. Análisis Económico)