OBJECTIVES: To examine relationships in mindfulness and illness acceptance and psychosocial functioning in patients with metastatic breast cancer and their family caregivers. SAMPLE & SETTING: 33 dyads from an academic cancer center in the United States. METHODS & VARIABLES: Participants completed questionnaires on mindfulness, illness acceptance, relationship quality, anxiety, and depressive symptoms. Dyadic, cross-sectional data were analyzed using actor-partner interdependence models. RESULTS: Greater nonjudging, acting with awareness, and illness acceptance among caregivers were associated with patients' and caregivers' perceptions of better relationship quality. Higher levels of these processes were associated with reduced anxiety and depressive symptoms in patients and caregivers. IMPLICATIONS FOR NURSING: Aspects of mindfulness and illness acceptance in dyads confer benefits that are primarily intrapersonal in nature. Nurses may consider introducing mindfulness and acceptance-based interventions to patients and caregivers with adjustment difficulties.