Coordination is a vital component in healthcare provision and teamwork. Relational coordination (RC) represents a type of informal coordination reinforced by communication and supportive relationships. It is an important concept in the study of interprofessional team performance and is associated with improved patient care outcomes. However, little is known about the specific relational characteristics that contribute to higher levels of RC. This study examined the association between social capital (resources embedded within relationships) and RC in outpatient clinics. RC was hypothesized to be predicted by social capital. In addition, social capital was hypothesized to be predicted by team tenure, and RC was hypothesized to be predicted by formal coordination mechanisms. A cross-sectional design was used to survey a random sample of 342 physicians and nurses from outpatient clinics. Study variables were measured using previously validated instruments with acceptable levels of reliability and validity. Structural equation modeling was used for hypothesis testing. Final analysis revealed a good fit of data to the hypothesized model (comparative fit index = 0.966; standardized root mean square residual = 0.0316). Results suggested that social capital predicted both factors of RC (b = 0.70 and 0.81, p < 0.001) and team tenure predicted social capital (b = 0.13, p < 0.05). Also, the association between team tenure and RC (b = 0.09, p < 0.05) was found to be partially mediated by social capital. Findings of this study suggest that characteristics within relational ties are predictive of informal coordination. The strength and pattern of these associations provide a better understanding in how relationships may facilitate interprofessional teamwork.