The Duchy of Sorrento was a small peninsular principality of the Early Middle Ages centred on the Italian city of Sorrento.
Originally, Sorrento was part of the Byzantine Duchy of Naples in the Dark Ages, but in the ninth century, along with Amalfi and Gaeta, it broke away from the Neapolitans to found its own ducatus (or republic). However, it mostly remained under Amalfi and only one independent duke is known from this period, a Sergius in the late ninth century.
In 1035, it was conquered by the Lombards under Guaimar IV of Salerno and bestowed on his younger brother Guy, who ruled it until the 1070s. Not long after that, it was annexed by the Normans.
In 1119, a certain Sergius undersigned a diploma of William II, Duke of Apulia, as "Prince of Sorrento."