PURPOSE: The purpose of this study was to evaluate the effects of lifestyle behaviors and health habits on the risk for acquiring pandemic influenza (H1N1) virus infection. MATERIALS AND METHODS: We conducted a case-control study in a secondary care hospital in South Korea between November 2009 and August 2010. We enrolled patients with H1N1 infection, as confirmed by a positive result of the real-time reverse transcriptase polymerase chain reaction assay; for each patient, we enrolled 4 age- and gender-matched controls with no history of H1N1 infection or severe acute respiratory illness during the H1N1 pandemic in South Korea (1:4 match). RESULTS: During the study period, 33 cases and 132 age- and gender-matched controls were enrolled. The case group had a higher percentage of current smokers (p<0.01), fewer subjects reporting regular physical activity (p=0.03), or regular vitamin supplementation (p<0.01), and more subjects reporting a higher annual incidence of the common cold (p=0.048) as compared to the control group. In the multivariable analysis, 2 factors were independently associated with the acquisition of H1N1 infection: current smoking [adjusted odds ratio (OR)=5.53; 95% confidence interval (CI), 1.60-19.16; p<0.01] and a higher annual incidence of the common cold (adjusted OR=1.24; 95% CI, 1.002-1.53; p=0.048). CONCLUSION: A current smoking status and a history of frequent colds were associated with an increased risk of acquiring H1N1 infection.