Background: In the general adult population, lymphopaenia is associated with an increased risk for hospitalisation with infection and infection-related death. The quality of evidence and strength of association between perioperative lymphopaenia across different surgical procedures and mortality/morbidity has not been examined by systematic review or meta-analysis. Methods: We searched MEDLINE, Embase, Web of Science, Google Scholar, and Cochrane databases from their inception to June 29, 2020 for observational studies reporting lymphocyte count and in-hospital mortality rate in adults. We defined preoperative lymphopaenia as a lymphocyte count 1.0e1.5Â10 9 L À1 . Meta-analysis was performed using either fixed or random effects models. Quality was assessed using the NewcastleeOttawa Scale. The I 2 index was used to quantify heterogeneity. The primary outcome was in-hospital mortality rate and mortality rate at 30 days. Results: Eight studies met the inclusion criteria for meta-analysis, comprising 4811 patients (age range, 46e91 yr; female, 20e79%). These studies examined preoperative lymphocyte count exclusively. Studies were of moderate to high quality overall, ranking >7 using the NewcastleeOttawa Scale. Preoperative lymphopaenia was associated with a threefold increase in mortality rate (risk ratio [RR]¼3.22; 95% confidence interval [CI], 2.19e4.72; P<0.01, I 2 ¼0%) and more frequent major postoperative complications (RR¼1.33; 95% CI, 1.21e1.45; P<0.01, I 2 ¼6%), including cardiovascular morbidity (RR¼1.77; 95% CI, 1.45e2.15; P<0.01, I 2 ¼0%), infections (RR¼1.45; 95% CI, 1.19e1.76; P<0.01, I 2 ¼0%), and acute renal dysfunction (RR¼2.66; 95% CI, 1.49e4.77; P<0.01, I 2 ¼1%). Conclusion: Preoperative lymphopaenia is associated with death and complications more frequently, independent of the type of surgery. Prospero registry number: CRD42020190702.