OBJECTIVES: Most of the adverse effects of Proton pump inhibitors (PPIs) were evaluated in inpatient setting and limited data exists regarding its adverse effects in community settings. This study examined the risk of pneumonia associated with the use of PPIs in community dwelling adults with Gastroesophageal Reflux Disease (GERD). METHODS: The study involved a retrospective cohort study design using Truven Health Analytics 2003-2004 MarketScan database. The study population included adults aged more than 18 years of age, diagnosed with GERD, identified anytime between July 1, 2003, and December 31 2003. The risk of pneumonia during the 12-month follow-up period was modeled using a time-varying Cox proportional model using monthly PPI exposure. Fractional Polynomial Cox proportional model was used to model the risk of pneumonia with cumulative duration of PPI use. Multiple sensitivity analyses were conducted to strengthen the study findings RESULTS: Analysis of MarketScan database revealed that there were 89,378 patients with GERD indication and among these, 60,207 (67.36%) patients were PPI users. Patients using PPIs were older, 49.65 (± 10.49) years, compared to patients not using PPIs, 46.93 (± 11.90) years and majority of the GERD patients were females (57.4%). Results from multivariate time varying Cox regression model revealed that PPI use was associated with 53% increased risk of pneumonia (HR, 1.53; 95% CI, 1.35-1.75). The findings were consistent across multiple sensitivity analyses. Fractional polynomial analysis revealed an initial decreased risk of pneumonia until 175 days of cumulative duration of PPI use and an increased risk after 175 days of cumulative PPI use was observed CONCLUSIONS: The study found an increased risk of pneumonia associated with PPI use among community dwelling adults with GERD diagnosis. Due to increasing safety concerns there is a need to be cautious in using PPIs for extended periods.