There are 5.8 million caregivers providing support to the infirm, disabled or elderly in the United Kingdom. Caregivers experience adverse physical and mental health outcomes and increased mortality. Low cost, effective interventions are needed to increase the wellbeing of caregivers. Written emotional disclosure (WED) has been shown to improve health in a range of populations. This systematic review and meta-analysis aimed to establish whether WED improves the psychological and physical health of caregivers. Searches were conducted in Medline, EMBASE, CINAHL, BNI, PsycINFO, Cochrane Library from 1986 to 2015. Ten trials investigating WED (625 participants) met the inclusion criteria. Results from four studies (n = 118) indicated that WED reduces trauma (SMD = −0.46, 95% CI -0.82, -0.09). Data from three studies (n = 102) suggest that WED improves general psychological health (SMD = −0.46, 95% CI -0.86, -0.06). There was no evidence that WED improves depression, anxiety, physical symptoms, quality of life or burden. Observations suggest WED may be more effective for caregivers of less than 5 years. Studies were highly heterogeneous in regards to caregiver age, relationship to care recipient, impairment of care recipient, follow up period and outcome measures, with high or unclear bias often observed. More rigorous RCTs, with clearly described interventions and standardised outcome measures, are needed to confirm these findings.