We investigate the role of relationship closeness, which is adapted from social network theory, in developmental relationships using a sample of 278 full-time working individuals. We theorize that personality, operationalized with the Five Factor Model, is associated with relationship closeness which is positively related to developer assistance received, which in turn is linked to objective and subjective measures of career success. In general, results supported our hypothesized model, although personality had direct effects on career success beyond the indirect effects through relationship closeness and developer assistance. The theoretical and practical implications are discussed. (Contains 1 figure and 2 tables.)