Why is Neuroticism so harmful to marriage and other intimate relationships? Given that such relationships generally involve a sexual component, the current longitudinal study explored whether the apparent negative impact of own and partner's Neuroticism on marriage could be explained by dissatisfaction with the sexual relationship. Just after their weddings, 72 couples reported their marital satisfaction, sexual satisfaction, and Neuroticism. One year later, they again reported their marital and sexual satisfaction. Own Neuroticism predicted lower levels of concurrent marital and sexual satisfaction among husbands and wives, declines in sexual satisfaction among husbands and wives, and declines in marital satisfaction among wives. Partner's Neuroticism predicted lower levels of concurrent marital satisfaction among husbands and wives, lower levels of concurrent sexual satisfaction among husbands, and declines in sexual satisfaction among husbands. Consistent with predictions, sexual satisfaction mediated every effect of own and partner Neuroticism on marital satisfaction. Results highlight the prominent role played by the sexual relationship in accounting for marital outcomes and thus suggest specific processes through which Neuroticism may affect the marriage.(PsycINFO Database Record (c) 2016 APA, all rights reserved)