Team-based health care assumes that groups representing multiple disciplines can work together to implement care plans that are comprehensive and integrated. It also assumes that professionals can function effectively in an interdependent relationship with members of other occupational groups. However, we know little about what makes effective team functioning. This article examines the factors related to health care team functioning, with specific emphasis on team demographic composition and size. Hierarchical linear modeling is used to analyze 106 Veterans Affairs (VA) hospitals. Results indicate that individuals who operate on more heterogenous and larger teams have lower perceptions of team functioning.