As noted recently by Jones et al., hypoglycemia is common in hospitalized patients with cystic fibrosis-related diabetes (CFRD) and is associated with an increase in readmission or death [1]. Though insulin therapy has been blamed for episodes of hypoglycemia, we noted ketonemia (elevated fingerstick 3-hydroxybutyrate) in several hospitalized patients with CFRD and hypoglycemia [2]; serum glucagon was low in one of these patients. Ketotic hypoglycemia is unlikely to be due to insulin therapy in this setting, and further study of this phenomenon is needed.