Objective: To determine the clinical characteristics in adults with confirmed pandemic influenza A (H1N1) infection 2009. Study Design: A case series. Place and Duration of Study: The study was carried out at the Department of Pulmonology and Critical Care, Military Hospital, Rawalpindi, from 1st December 2009 to 30th May 2010. Methodology: Thirty six adults with confirmed 2009 pandemic H1N1 infection by reverse transciptase polymerase chain reaction (RT-PCR) were included in the study. All patients were followed in-hospital and clinical features, laboratory and radiological investigations and management data was collected on a pre-designed patient data collection form. Results: Mean age was 34.24±13.92 years with 61.1% females. Seventeen (47.2%) had at least one risk factor for complications with 2009 H1N1 infection; namely obesity in 19.4%, pregnancy in 8.3%, COPD in 5.6%, cardiac failure in 5.6%, chronic liver disease in 5.6%, Diabetes mellitus in 5.6%, immunosuppression in 2.3%, smoking in 25%. Fever (97.2%), cough (97.2%), rhinnorhea (80.6%), and shortness of breath (58.3%) were the commonest symptoms. Radiographic abnormalities were interstial/reticular infiltrates (30.6%), patchy consolidations (11.1%) and reticular shadows with areas of consolidation (25%). PaO2/FiO2 ratio was less than 200 in 27.8% cases. Thirty six percent cases had creatinine kinase (CK) levels greater than 400 U/L and lactate dehydrogenase (LDH) levels higher than 1000 U/L. Twenty seven percent cases were managed in ICU and 16.7% cases died during hospital stay. Conclusion: The 2009 pandemic H1N1 virus infection had a wide clinical spectrum with a potential to cause high morbidity and mortality. Early empirical antiviral therapy for hospitalized suspected influenza A (H1N1) is vital to prevent the rapid disease progression.