Spousal similarity and its consequences are widely studied, but methodologically challenging topics. We employed Response Surface Analysis to examine similarity along political attitudes, personal values, and personality traits. Opposite-sex couples (624 individuals) expecting a child were recruited. Spouses were highly similar regarding their political attitudes and moderately similar regarding trait Openness and the personal values Universalism and Tradition. Similarity for other traits and values was weak (e.g. Conscientiousness, Power values) or non-existent (e.g. Neuroticism, Benevolence values). Similarity in conservative vs. liberal attitudes was non-linear: a conservative-conservative union was most common. Women’s relationship satisfaction was related to similarity in left-right and liberal-conservative political attitudes, and both partners’ satisfaction was related to similarity in Self-Direction values. Similarity in personality traits was unrelated to relationship satisfaction.