Background: Previous systematic reviews have assessed the effect of critical care outreach services, but none have focused solely on nurse-led services. Aim: To perform a systematic review examining the impact of nurse-led critical care outreach services on inpatient mortality rates as the primary outcome. Secondary outcomes include arrest call rates and patient length of stay. Methods: A comprehensive search of several electronic databases was carried out, including the Cumulative Index to Nursing and Allied Health Literature and Medline. Non-catalogued literature was searched, and contact was made by e-mail with expert authors. All studies were in the English language, and although heterogeneous in design, only quantitative data were extracted for analysis. All included studies were assessed for quality using recognized quality appraisal tools. Meta-analysis was not possible because of heterogeneity. Results: Ten studies involving almost 72 000 participants were identified. The reduction in mortality rates with nurse-led critical care outreach services was reported to be 80%, but the statistical significance was low -four studies showed reductions ranging from 0⋅1% to 0⋅22%. Greater statistical significance was reported in arrest call rates, with two studies claiming decreased rates of 58⋅7% and 29⋅6%. Two studies reported a decrease in patient length of stay -the findings of a third study were equivocal. Half of the included studies scored poorly in terms of quality and validity, and all were single-centre studies, thereby limiting generalisability. Conclusion: Nurse-led critical care outreach services demonstrate benefits in terms of patient care and reduction in adverse events. Higher-quality research, including multicentre randomized controlled trials, with meta-analysis is recommended. Relevance to clinical practice: Nurse-led critical care outreach services have the potential to improve patient outcomes. Uniformity of team composition and nomenclature would benefit data collection and reporting.