Background Chronic obstructive pulmonary disease (COPD) is a common, preventable and curable disease characterized by persistent respiratory symptoms and persistent obstructive ventilation disorders that occur as a result of airway disorders/alveolar abnormalities, most often as part of exposure to inhalation of harmful particles or gases. The disease is progressive and significantly affects the patient's quality of life. Aim The aim of the research was to determine the effectiveness of pulmonary rehabilitation in patients with COPD in the Clinical Hospital Center Zagreb. The specific objectives were to determine the general condition of COPD patients before and after pulmonary rehabilitation and whether there are differences in the results of male and female gender, depending on the age before and after pulmonary rehabilitation using the CAT questionnaire (COPD assessment test). Methods A retrospective study was conducted at the Clinical Hospital Center Zagreb, KPB Jordanovac at the Respiratory Rehabilitation Department. Data were analyzed from January 2019. to November 2022. Data from the CAT questionnaire, which examined patients before and after pulmonary rehabilitation, and socio-demographic data from the database, were used. Results 107 patients of both sexes were included in the analysis. Most of the patients were male (54.2%), the median age was 66 years. A statistically significant difference was found in the results of measuring the general condition of COPD patients before and after pulmonary rehabilitation; significantly lower results of the CAT test are shown by the subjects after the rehabilitation, i.e. they show a significantly better general condition after the rehabilitation. Also, a significant difference was found in the results of measuring the general condition of COPD patients before and after pulmonary rehabilitation. Conclusion The research confirmed the effectiveness of pulmonary rehabilitation in patients with COPD.