Background: Regaining pre-hospitalization activity levels is only achieved in 30-50% of older patients. Extra physiotherapy time has been proven to improve functional outcome and shorten length of stay, but is costly. Considering their key role in caring for older people, involving informal caregivers in rehabilitation might further improve functional performance. Aim: To determine if in-hospital or post discharge caregiver involvement can increase functional performance in older adults. The secondary aim was to determine if caregiver involvement can influence, quality of life of patient and caregiver, medical costs, readmission rate, discharge location, and mortality. Design: Systematic review with narrative synthesis. Methods: The electronic bibliographic databases MEDLINE, Embase, CINAHL, Cochrane and Web of Science were searched for (quasi) experimental and observational studies, with the following inclusion criteria; caregiver involvement regarding functional performance, mean age over 65 years, admitted to a hospital unit and subsequently discharged to their home setting. Risk of bias was assessed with the Rob 2 (randomized trials) and the ROBINS-1 tool (non-randomized studies). Results: Eight studies of an initial 4683 were included: four randomized controlled trials, one prospective cohort study, one non-randomized controlled trial, one subgroup analysis of an RCT and one prospective pre-post study. All but one study included patients with stroke. Three types of caregiver interventions could be distinguished: a care pathway (inclusion of caregivers in the process of care), education on stroke and teaching of bed-side handling-skills, and caregiver-mediated exercises. The one study evaluating the care pathway reported 24.9% more returns home in the intervention group. Studies evaluating the effect of education and bed-side handling-skills reported higher effect sizes for several outcomes with increasing session frequency. All studies with caregiver-mediated exercises showed beneficial effects on functional performance, immediately after the intervention and within 3 months follow-up. Conclusion: The findings of this review suggest that involvement of caregivers in the rehabilitation of older adults leads to better functional performance up to 3 months after initiation. However, evidence is low and mainly focusing on stroke.