Background: Bacterial co-infection is an important contributor to morbidity and mortality during influenza pandemics .We investigated the incidence, risk factors and outcome of patients with influenza A H1N1 pneumonia and bacterial co-infection. Methods: Prospective observational study of consecutive hospitalized patients with influenza A H1N1 virus and community-acquired pneumonia (CAP). We compared cases with and without bacterial co-infection. Results: The incidence of influenza A H1N1 infection in CAP during the pandemic period was 19% (. n, 667). We studied 128 patients; 42(33%) had bacterial co-infection. The most frequently isolated bacterial pathogens were . Streptococcus pneumoniae (26, 62%) and . Pseudomonas aeruginosa (6, 14%). Predictors for bacterial co-infection were chronic obstructive pulmonary disease (COPD) and increase of platelets count. The hospital mortality was 9%. Factors associated with mortality were age ≥65 years, presence of septic shock and the need for mechanical ventilation. Although patients with bacterial co-infection presented with higher Pneumonia Severity Index risk class, hospital mortality was similar to patients without bacterial co-infection (7% . vs. 11%, respectively, . p = 0.54). Conclusion: Bacterial co-infection was frequent in influenza A H1N1 pneumonia, with COPD and increased platelet count as the main predictors. Although associated with higher severe scales at admission, bacterial co-infection did not influence mortality of these patients.