Marcetelli is a comune (municipality) in the Province of Rieti in the Italian region of Latium, located about 60 km northeast of Rome and about 25 km southeast of Rieti. Marcetelli borders the following municipalities: Ascrea, Collalto Sabino, Collegiove, Paganico Sabino, Pescorocchiano, Varco Sabino. By number of inhabitants, it is the smallest municipality in Lazio and among the smallest in Italy.