Abstract
A newborn boy with Rubinstein–Taybi syndrome who had profound neonatal hypoglycemia is presented. The infant was a discordant fraternal twin with intrauterine growth retardation. The hypoglycemia was due to transient hyperinsulinemia, a condition often seen in small‐for‐gestational‐age infants. Neonatal hypoglycemia may be common in infants with Rubinstein–Taybi syndrome, especially if they also have intrauterine growth retardation.