Context: The Advisory Committee on Immunization Practices (ACIP) recommends annual influenza vaccination for children with certain chronic medical conditions to prevent serious complications of influenza infection. Little is known about the relative contribution of each of these chronic medical conditions to the development of serious influenza associated complications. Objective: To identify chronic medical conditions that are associated with respiratory failure in children hospitalized with communityacquired laboratory confirmed influenza. Design, Setting, and Patients: A retrospective cohort study of patients aged 21 years or younger hospitalized at The Children s Hospital of Philadelphia with community acquired laboratory confirmed influenza during 4 consecutive influenza seasons (June 2000 through May 2004). We examined 9 ACIP designat ed high risk chronic medical conditions and 3 additional chronic medical conditions (neurological and neuromuscular disease [NNMD], gastroesophageal reflux disease [GERD], and history of prematurity) that in recent studies have been associated with influenza hospitalization and severe influenza related complications. Main Outcome Measures: Rate and odds ratio (OR)- of respiratory failure, defined as need for mechanical ventilation. Results: Of 745 children hospitalized with community acquired laboratory confirmed influenza, 322 (43% ) had 1 or more ACIP designated high risk chronic medical conditions. Neurological and neuromuscular disease, GERD, and history of prematurity were present in 12% , 14% , and 3% , of children, respectively. Thirty two children (4.3% ) developed respiratory failure. In multivariate logistic regression analyses, conditions associated with respiratory failure included NNMD (OR, 6.0; 95% confidence interval [CI], 2.7- 13.5), chronic pulmonary disease other than asthma (OR, 4.8; 95% CI, 1.5- 15.1), and cardiac disease (OR, 4.0; 95% CI, 1.6- 10.2). The predicted probabilities of respiratory failure derived from the multivariate model were 12% (95% CI, 7% - 20% ), 9% (95% CI, 3% - 23% ), and 8% (95% CI, 4% - 18% ) for children with NNMD, chronic pulmonary disease, and cardiac disease, respectively. Conclusions: These results support the ACIP s recent decision to add NNMD to the list of conditions for which annual influenza vaccine is recommended in children. Neurologists and primary care pediatricians should be alerted to the increased risk of respiratory failure and the importance of influenza vaccination in children with NNMD. Context: The Advisory Committee on Immunization Practices (ACIP) Recommend annual influenza vaccination for children with certain chronic medical conditions to prevent serious complications of influenza infection. Little is known about the relative contribution of each of these chronic medical conditions to the development of serious influenza Objective, To identify chronic medical conditions that are associated with respiratory failure in children hospitalized with community acquired laboratory-confirmed influenza. Design, Setting, and Patients: A retrospective cohort study of patients aged 21 years or younger hospitalized at The Children s Hospital of Philadelphia with community-acquired laboratory-confirmed influenza during 4 consecutive influenza seasons (June 2000 through May 2004). We examined 9 ACIP-designat high-risk chronic medical conditions and 3 additional chronic medical conditions (neurological and neuromuscular disease [NNMD], gastroesophageal reflux disease [GERD], and history of prematurity) that in recent studies have been associated with influenza hospitalization and severe influenza-related complications. Main Outcome Measures: Rate and odds ratio (OR) - of respiratory failure, defined Results: Of 745 children hospitalized with community-acquired laboratory confirmed influenza, 322 (43%) had 1 or more ACIP-designated high-risk chronic medical conditions. Neurological and neuromuscular disease, GERD, and history of prematurity In multivariate logistic regression analyzes, conditions associated with respiratory failure included NNMD (OR, 6.0; 95%) were present in 12%, 14%, and 3%, of children, respectively. confidence interval [CI], 2.7- 13.5), chronic pulmonary disease other than asthma (OR, 4.8; 95% CI, 1.5-15.1), and cardiac disease probab ilities of respiratory failure derived from the multivariate model were 12% (95% CI, 7% -20%), 9% (95% CI 3% -23%), and 8% children with NNMD, chronic pulmonary disease, and cardiac disease, respectively. Conclusions: These results support the ACIP’s recent decision to add NNMD to the list of conditions for for annual influenza vaccine is recommended in children. Neurologists and primary care pediatricians should be alerted to the increased risk of respiratory failure and the importance of influenza vaccination in children with NNMD.