After two decades of widespread use, proton pump inhibitors are considered to have a very well-documented and acceptable adverse effect profile in the short-term. Yet adverse effects continue to emerge. In particular, epidemiological studies conducted over the past 10-12 years showed an increased incidence of fractures. New data now point to an increased risk of bacterial pneumonia. A Korean meta-analysis published in 2011 showed a statistically significant increase in the risk of bacterial pneumonia in patients taking proton pump inhibitors, with an odds ratio of 1.27 (95% confidence interval (95% CI): 1.11 to 1.46). The increase in community-acquired pneumonia was also statistically significant, with an odds ratio of 1.34 (95% CI: 1.14 to 1.57). This is consistent with the results of a meta-analysis published in 2010, which gave an odds ratio of 1.36 (95% CI: 1.12 to 1.65). The increase in the frequency of bacterial pneumonia was highest during the first week of treatment, with an odds ratio of 3.95 (95% CI: 2.86 to 5.45). Subsequent studies have provided conflicting results. Possible mechanisms include bacterial passage into the lungs after colonisation of the upper gastrointestinal tract resulting from the reduction in gastric acidity; bacterial overgrowth in the lungs due to a change in the pH of respiratory secretions; and impaired neutrophil phagocytic function. The available data suggest that proton pump inhibitors play a role in the increased frequency of bacterial pneumonia in treated patients. Similar data implicating H2 receptor antagonists and the proposed mechanism (acid suppression) imply that there are no alternative acid-suppressive medications. This risk of pneumonia is yet another reason not to trivialise the use of proton pump inhibitors. These drugs should only be used when the likely benefits clearly outweigh the potential harms.