To the Editor In an investigation to quantify the association between the use of proton pump inhibitors (PPIs) and incidence of chronic kidney disease (CKD) in a population-based cohort, Lazarus et al1 concluded that PPI use is associated with a higher risk of CKD. In this sense, we would like to express concern about the baseline characteristics of patients who are prescribed PPIs that could constitute an important source of bias. Indeed, PPI users were more likely than nonusers to have a greater burden of prescribed medications and comorbidities that influence the baseline risk of CKD for reasons unrelated to their PPI use.