CWith an area of just 3.7 square kilometers and the nearby islet of Vivara (0.4 km ²) is considered the smallest island in the Gulf of Naples; the perimeter, extremely rugged, measuring about 16 km and it covers the whole municipal area the island.

The highest point is the hill of Terra Murata (91 m), topped by a fortified village of medieval origin.

Its coasts, low and sandy in some areas, in other places on the sea, give rise to different bays and headlands that offer shelter to small navigation and allowed the birth of three marinas on the north, east and south side of the island. Most of its coastline is included in the protected natural area "Regno di Nettuno ".

Traditionally, the town is divided into nine districts: Terra Murata (the oldest town), Corricella (a quaint fishing village), Sent'cò with the commercial port of Marina Grande, San Leonardo, Santissima Annunziata, Sant'Antuono,  Sant’Antonio and Chiaiolella (a marina in the south).