OBJECTIVE: The aim of the study was to describe the prevalence of comorbidities in patients with severe obesity in Poland and to assess the relationship between the diagnosis of chronic diseases and total weight lost after bariatric surgery in 1 year observation. PATIENTS AND METHODS: The current study is a retrospective analysis that included medical records of 601 patients with data on body weight before and 1 year after bariatric surgery. The total weight loss was calculated as the difference between the initial body weight and body weight after 1 year, divided by the initial body weight, multiplied by 100. The total weight loss was calculated separately for body weight at admission for the surgery (%WL) and maximum recorded body weight (%maxWL). Data on history of all recorded in medical documentation chronic diseases were used. The associations between the presence of chronic diseases at baseline and total weight loss were assessed using multivariable linear regression. RESULTS: Hypertension was the most common chronic disease (71.2%). Patients with hypertension, metabolic syndrome, and chronic obstructive pulmonary disease (COPD) had significantly higher %WL and %maxWL, while those with osteoarthritis and gastroesophageal reflux disease (GERD) had lower %WL and %maxWL. After adjusting for age, sex, and initial body mass index (BMI), the presence of metabolic syndrome and COPD was positively associated with %WL (respectively, beta = 2.405; 95% CI: 0.195-4.615 and beta = 6.522; 95% CI: 1.094-11.951) and with %maxWL (respectively, beta = 2.389; 95% CI: 0.249-4.528 and beta = 6.281; 95% CI: 1.038-11.524). All other diseases and total number of comorbidities were not related to total weight loss. CONCLUSION: Among patients undergoing bariatric surgery, obesity-related comorbidities were highly prevalent at baseline and did not adversely affect postoperative weight loss. Specifically, the presence of metabolic syndrome and COPD was independently associated with a greater 1-year total weight loss.