This study analyses the importance of partner status and partner's education, adjusted for own education, on self-assessed health, smoking and excessive alcohol consumption. The relationship between socio-economic factors and health-related outcomes is traditionally studied from an individual perspective. Recently, applying social-ecological models that include socio-economic factors on various social levels is becoming popular. We argue that partners are an important influence on individual health and health-related behaviour at the household level. Therefore, we include partners in the analysis of educational health inequalities. Using data of almost 40,000 individuals (with almost 15,000 Dutch cohabiting couples), aged 25-74 years, who participated in the Netherlands Health Interview Survey between 1989 and 1996, we test hypotheses on the importance of own and partner's education. We apply advanced logistic regression models that are especially suitable for studying the relative influence of partners' education. Controlled for own education, partner's education is significantly associated with self-assessed health and smoking, for men and women. Accounting for both partners' education the social gradient in self-assessed health and smoking is steeper than based on own or partner's education alone. The social gradient in health is underestimated by not considering partner's education, especially for women.