This study investigated the effectiveness of a structured telephone intervention for caregivers of people diagnosed with poor prognosis gastrointestinal cancer to improve psychosocial outcomes for both caregivers and patients. Caregivers of patients starting treatment for upper gastrointestinal or Dukes D colorectal cancer were randomly assigned (1:1) to the Family Connect telephone intervention or usual care. Caregivers in the intervention group received four standardized telephone calls in the 10 weeks following patient hospital discharge. Caregivers' quality of life (QOL), caregiver burden, unmet supportive care needs and distress were assessed at 3 and 6 months. Patients' QOL, unmet supportive care needs, distress and health service utilization were also assessed at these time points. Caregivers (128) were randomized to intervention or usual care groups. At 3 months, caregiver QOL scores and other caregiver-reported outcomes were similar in both groups. Intervention group participants experienced a greater sense of social support (p = .049) and reduced worry about finances (p = .014). Patients whose caregiver was randomized to the intervention also had fewer emergency department presentations and unplanned hospital readmissions at 3 months post-discharge (total 17 vs. 5, p = .01). Conclusions: This standardized intervention did not demonstrate any significant improvements in caregiver well-being but did result in a decrease in patient emergency department presentations and unplanned hospital readmissions in the immediate post-discharge period. The trend towards improvements in a number of caregiver outcomes and the improvement in health service utilization support further development of telephone-based caregiver-focused supportive care interventions.