The Somogyi effect postulates that nocturnal hypoglycaemia causes fasting hyperglycaemia attributable to counter-regulatory hormone release. Although most published evidence has failed to support this hypothesis, this concept remains firmly embedded in clinical practice and often prevents patients and professionals from optimizing overnight insulin. Previous observational data found lower fasting glucose was associated with nocturnal hypoglycaemia, but did not assess the probability of infrequent individual episodes of rebound hypoglycaemia. We analysed continuous glucose monitoring data to explore its prevalence.