The present study reports on the scope and size of sex differences in 30 personality facet traits, using one of the largest US samples to date (N = 320,128). The study was one of the first to utilize the open access version of the Five-Factor Model of personality (IPIP-NEO-120) in the large public. Overall, across age-groups 19–69 years old, women scored notably higher than men in Agreeableness (d = 0.58) and Neuroticism (d = 0.40). Specifically, women scored d > 0.50 in facet traits Anxiety, Vulnerability, Openness to Emotions, Altruism, and Sympathy, while men only scored slightly higher (d > 0.20) than women in facet traits Excitement-seeking and Openness to Intellect. Sex gaps in the five trait domains were fairly constant across all age-groups, with the exception for age-group 19–29 years old. The discussion centers on how to interpret effects sizes in sex differences in personality traits, and tentative consequences. © 2018 Elsevier Ltd