OBJECTIVE: To review all available original publications on the harms and benefits of subcutaneous (SC) hydration in older patients. DESIGN: Systematic review and meta-analysis. PARTICIPANTS: All studies on SC hydration in older patients without restrictions on design or language. MEASUREMENTS: The Medline, Embase, CINAHL, Cochrane Central Register of Controlled Trials, and Web of Science databases and trial registries were searched from inception to November 5, 2019, and two reviewers independently extracted the data and assessed the risk of bias of individual outcomes. RESULTS: Thirty-one publications from 29 studies met the eligibility criteria. The data from six randomized controlled trials were used for the meta-analyses. The subgroup analysis including only the studies with the lowest risk of bias showed that SC hydration was associated with fewer adverse effects than intravenous (IV) hydration (risk ratio (RR) = 0.69; 95% confidence interval (CI) = 0.53-0.88; P = .003; n = 4; I(2) = 0.0%; 545 infusions in each group). In absolute numbers, patients treated with SC hydration had an incidence rate of 90 adverse effects per 1,000 infusions versus 130 adverse effects per 1,000 infusions (95% CI = 102-169) with IV hydration. Secondary outcomes comparing IV with SC hydration showed that SC was 3.2 minutes faster to set up and markedly reduced the risk of agitation (RR = 0.42; 95% CI = 0.22-0.79; P = .007; I(2) = 65%; n = 3); however, SC hydration delivered a lower volume of fluid and was less efficient at reducing serum osmolality (s-osmolality). CONCLUSIONS: SC hydration is safer than IV hydration and potentially reduces the risk of agitation, but it is less effective. SC hydration should be available as an alternative to IV hydration when treating older patients for mild-to-moderate dehydration. More high-quality studies are needed in the field to increase the confidence in the estimates.