Background: This prospective study aims to determine whether preoperative stair-climbing tests (SCT) predict postoperative pulmonary complications (PPC) better than self-reported poor functional capacity (SRPFC) in patients with known or suspected COPD. Methods: A total of 320 patients undergoing scheduled for major non-cardiac surgery, 240 with verified COPD and 80 with GOLD key indicators but disproved COPD, underwent preoperative SRPFCand SCT and were analyzed. Least absolute shrinkage and selection operator (LASSO) regression was used for variable selection. Two multivariable regression models were fitted, the SRPFCmodel (baseline variables such as sociodemographic, surgical and procedural characteristics, medical preconditions, and GOLD key indicators plus SRPFC) and the SCT model (baseline variables plus SCTPFC). Results: Within all stair-climbing variables, LASSO exclusively selected self-reported poor functional capacity. The cross-validated area under the receiver operating characteristic curve with bias-corrected bootstrapping 95% confidence interval (95% CI) did not differ between the SRPFCand SCT models (0.71; 0.65–0.77 for both models). SRPFCwas an independent risk factor (adjusted odds ratio (OR) 5.45; 95% CI 1.04–28.60;p= 0.045 in the SRPFCmodel) but SCTPFCwas not (adjusted OR 3.78; 95% CI 0.87–16.34;p= 0.075 in the SCT model). Conclusions: Our findings indicate that preoperative SRPFCadequately predicts PPC while additional preoperative SCTs are dispensable in patients with known or suspected COPD.