Evidence regarding the relationship between the type of anaesthesia and length of hospital stay is controversial. Therefore, the objective of this research was to investigate whether the type of anaesthesia was independently related to the length of hospital stay in patients undergoing unilateral total knee arthroplasty (TKA) after adjusting for other covariates.The present study was a cohort study. A total of 2622 participants underwent total knee arthroplasty (TKA) at a hospital in Singapore from 2013 to 1-1 to 2014-6-30. The target independent variable and the dependent variable were two types of anaesthesia and length of hospital stay, respectively. The covariates included age, BMI, hemoglobin (Hb), length of stay (LOS), duration of surgery, sex, ethnicity, American Society of Anesthesiologist (ASA) Status, smoking, obstructive sleep apnea (OSA), diabetes mellitus (DM), DM on insulin, ischemic heart disease (IHD), congestive cardiac failure (CCF), cerebrovascular accident (CVA), creatinine > 2 mg/dl, day of week of operation. Multivariate linear and logistic regression analyses were performed on the variables that might influence the choice of the two types of anaesthesia and the LOS. This association was then tested by subgroup analysis using hierarchical variables.The average age of 2366 selected participants was 66.57 ± 8.23 years old, and approximately 24.18% of them were male. The average LOS of all enrolled patients was 5.37 ± 4.87 days, 5.92 ± 6.20 days for patients receiving general anaesthesia (GA) and 5.09 ± 3.98 days for patients receiving regional anaesthesia (RA), P < 0.05. The results of fully adjusted linear regression showed that GA lasted 0.93 days longer than RA (β = 0.93, 95% CI (0.54, 1.32)), P < 0.05. The results of fully adjusted logistic regression showed that LOS > 6 days was 45% higher for GA than for RA (OR = 1.45, 95% CI (1.15, 1.84)), P < 0.05. Through the subgroup analysis, the results were basically stable and reliable.Our study showed that GA increased the length of stay during unilateral TKA compared with RA. This finding needs to be validated in future studies.© 2021. The Author(s).