During the last 2 years, 597 cases of chronic obstructive pulmonary disease (COPD) exacerbated due to respiratory infections were treated in our department. Eighty-eight (14.7%) of them suffered from diabetes mellitus (DM). Thirty-four had insulin-dependent DM and 54 non-insulin-dependent DM. In these groups, we studied the duration of hospitalization, their clinical features, chest X-rays, blood tests (white blood cells, erythrocyte sedimentation rate), blood gases and the sputum culture for bacteria. The paired t test was used for statistical analysis. Our results showed that the mean duration of hospitalization in patients with DM was 10.76 +/- 2.7 days (X +/- SD), whereas for patients without DM it was 8.53 +/- 1.9 days. Patients with insulin-dependent DM had a mean hospitalization of 15.63 +/- 3.6 days, which was statistically significant in relation to the group without DM (p < 0.0001). As for the chest X-rays, clinical features, blood tests and blood gases, no statistically significant differences were found among the groups. The sputum culture for bacteria showed that in patients with insulin-dependent DM the isolation of gram-negative bacteria was 51.6%, which was statistically significant in relation to the group without DM, where it was 27.3% (p < 0.0001). In conclusion, a significant percentage of patients with COPD suffers from DM. Patients with insulin-dependent DM and COPD with respiratory infections were found to have longer periods of hospitalization and a larger percentage of gram-negative bacteria in the sputum culture.