Personality has yet to be examined as an indirect yet powerful determinant of the diversity of personal social networks that is independent of preference- and population-based mechanisms. I use the 2004 General Social Survey to illustrate how dispositional optimism shapes core discussion network size as well as demographic heterophily among core ties. I find that optimism is associated with enhanced network size as well as ties among nonkin and across lines of age, education, and race. Following these results, I urge closer attention to personality as it dynamically shapes the social structure of opportunities and resources.