Background. Hyperinsulinemic hypoglycemia with neuroglycopenia is a rare complication of Roux-en-Y gastric bypass (RYGB). We hypothesized that continuous glucose monitoring (CGM) would be useful to characterize glycemic variability after RYGB. Methods. CGM and mixed meal tolerance testing (MMTT) were performed on sixteen post-RYGB subjects, ten with a history of neuroglycopenia on medical treatment and six asymptomatic controls. Results. 9 of 10 subjects with neuroglycopenia developed hypoglycemia defined by glucose <70 mg/dL on CGM, and 3 of 9 on MMTT. In asymptomatic subjects, 3 of 6 had asymptomatic hypoglycemia during CGM, and 3 of 5 on MMTT. Therefore, the sensitivity and specificity to detect clinically significant hypoglycemia was 90% and 50% for CGM and 33% and 40% for MMTT. Conclusions. Asymptomatic hypoglycemia after RYGB is more frequent than commonly recognized. For clinicians evaluating patients for postbypass neuroglycopenia, CGM may be a valuable diagnostic tool.