Aim The aim of the present study was to determine the prevalence of comorbidities in very elderly patients hospitalized as a result of acute respiratory diseases and to analyze sex‐specific differences, and to examine the effects of these comorbidities on their treatment outcomes. Methods A total of 3316 patients were admitted to our pulmonary inpatient clinic between 2009 and 2011, and 243 of them (aged over 80 years) with acute respiratory disease were included in our study. Data were retrospectively collected, and included demographic features, comorbidities, laboratory findings, length of hospital stay and in‐hospital mortality. Results In total of 243, 144 patients (59.3%) were men and 99 patients (40.7%) were women. The mean age was 84 ± 3 years. The prevalence of comorbidity was 75.7% (n = 184). The most common comorbid disease in patients with chronic obstructive pulmonary disease was congestive heart failure (32.9%), and it was chronic obstructive pulmonary disease (49.4%) in patients with pneumonia. The rate of having one comorbidity was 58.2% (n = 107) and 35.3% (n = 65) had two. Approximately half (52.6%) of the in‐hospital deaths occurred within the first 48 hours of hospitalization. The number of comorbidities was higher in the deceased patients compared with the living patients (P = 0.01). Conclusions The present study showed that the majority of our patients had at least one comorbidity. The first 48 hours of hospitalization was very important, especially for the patients with comorbidities, to determine the need for intensive care unit and prognosis. The coexistence of comorbidities can increase the risk of mortality in the elderly. Geriatr Gerontol Int 2016; 16: 791–796.