Recovery from a mild-to-moderate traumatic brain injury (TBI) is a challenging process for injured persons and their families. Guided by attachment theory, we investigated whether relationship conflict, social support, or sense of belonging were associated with psychological functioning. Community-dwelling persons with TBI (N = 75) and their relatives/significant others (N = 74) were surveyed on relationship variables, functional status, and TBI symptom severity. Results from this cross-sectional study revealed that only sense of belonging was a significant predictor of postinjury psychological functioning, although interpersonal conflict approached significance. No relevant preinjury or injury-related variables impacted these relationships, except marital status. Our findings suggest that interventions targeting strengthening the injured persons' sense of belonging and lowering interpersonal conflict may benefit those living with TBI. (Contains 1 figure and 2 tables.)