Background: Covid-19 is associated with hospitalization and high mortality rate. Previous studies suggested higher mortality rate in Covid-19 patients with comorbidities, however controversies among different studies about the burden of comorbidity were found. Objective: To identify what and to what extend comorbid diseases are associated with hospitalized Covid-19 patients’ mortality. Methods: A retrospective single-center study was conducted using anonymized HIS administrative data for 71330 patients in the university hospital "Saint Marina"-Varna, Bulgaria, for the period 14/06/2020–31/12/2021. Non-parametric tests and logistic regression were applied at α = .05; 95%CI. Results: Up to seven comorbidities per patient were registered, 9036 for discharged, 4967 for deceased Covid-19 patients. Comorbidities registered for < 30(1.5%) patients were discarded. From 8319 Covid-19 patients, 1809(21.7%) died - 54.3% male; mean age 70.7(SD=11.38); 130(7.2%) had seven, 207(11.4%) had no comorbidities. Deceased comorbid patients had more comorbidities (z=23.314; p<.001), were older (z=15.345; p<.001) and had shorter hospital stay (z=15.749; p<.001). Infectious/Parasitic diseases (A) were registered for 157(8.7%) patients, (157 diseases: A41.9; A04.7;A94.1); cardiovascular diseases (I) registered for 1266(70%) patients (2430 diseases: I11.9;I20.8;I11.0;I48;I50.1;I69.3;I67.9;I13.2;I25.8;I50.1); respiratory diseases (J) - registered for 617(34.1%) patients (651 diseases: J96.0;J80); renal diseases (N) - registered for 192(10.6%) patients (283 diseases: N18.8; N18.9;N40); endocrine/metabolic diseases (E) - registered for 478(26.5%) patients (643 diseases: E11.9;E11.4;E11.7;E78.4); malignant neoplasms (C) - registered for 89(4.9%) patients (92 diseases). Patients with (A),(J),(I),(N),(E) and (C) comorbidities had higher odds of dying (ORA = 20.284; 95%CI=12.371–33.256); (ORJ = 4.08; 95%CI=3.604–4.618); (ORI =2.752; 95%CI=2.461–3.077), (ORN = 2.866; 95%CI=2.359–3.481), (ORE=1.539; 95%CI=1.362–1.737); (ORC=1.633; 95%CI=1.265–2.107), correspondingly. Conclusions: Death with Covid-19 was associated with sepsis, pulmonary, cardiovascular, endocrine, renal and cancer comorbidities, however with lower odds. Monitoring Covid-19 patients for comorbidities is highly recommended to prevent mortality. HIS administrative data can be used for analyses of hospital comorbidity and mortality in pandemics and disasters.