Proton pump inhibitors (PPIs) are extensively prescribed drugs usually used for a long period. Recent reports linked PPI use with development of hypomagnesemia. However, there is still uncertainty regarding risk of hypomagnesemia in outpatients who were on long-term PPI use. Thus, we aimed to evaluate frequency of hypomagnesemia among a well-defined outpatient patient cohort with no other possible risk factors affecting serum magnesium levels. This was a case-control study carried out at the outpatient gastroenterology clinic of a University hospital. Patients who were on PPI therapy for at least 6 months without diuretic use and chronic kidney disease were included. Patients who were subjected to the same inclusion and exclusion criteria and not using PPI were included as control subjects. One hundred fifty-four patients and 84 control subjects were included. The mean duration of PPI use was 27.5 ± 2.5 months. Mean serum magnesium levels of PPI users and nonusers were 2.17 ± 0.20 mg/dL and 2.19 ± 0.15 mg/dL, respectively. None of the patient had a serum magnesium level below laboratory lower range of 1.7 mg/dL. Our results showed that for typical gastroenterology outpatient clinic patients with no other risk factors affecting serum magnesium levels, long-term PPI use did not affect serum magnesium levels.