INTRODUCTION The COPD Assessment Test (CAT) is a standardized patient–completed tool dedicated to assessment of symptom severity. While the Polish CAT version has been used for a few years, it has not been validated so far. OBJECTIVES The aim of the study was to validate the Polish‑language version of the CAT questionnaire by assessing its reproducibility and reliability. PATIENTS AND METHODS Validation of the Polish‑language version of the CAT questionnaire was a substudy of the international multicenter observational cross‑sectional POPE survey of patients with chronic obstructive pulmonary disease (COPD) in Central and Eastern European countries. The study was completed in 395 outpatients with stable disease at least 4 weeks before the survey. Validation was performed with the use of the Spearman correlation and Cronbach α coefficients, Cohen κ test, and the Bland–Altman procedure. RESULTS The internal consistency assessed by the Cronbach α coefficient was 0.87 for the questionnaire and 0.84 to 0.86 for its separate items. The repeatability of the questionnaire was good to very good (Cohen κ, 0.76–0.85; P <0.01). The Spearman coefficient for the sum of scores of test–retest responses was 0.95 (P <0.01). The Bland–Altman analysis revealed very good test–retest and interrater reliability, with the mean difference between test I and test II results of –0.556 (95% CI, –0.345 to 0.767). CONCLUSIONS The Polish version of the CAT questionnaire is a reproducible and reliable instrument for evaluation of patients with COPD and should be recommended for use in clinical practice.