For centuries, scientists have been inspired by island ecosystems in terms of their biodiversity and physical environment. Because freshwater and terrestrial ecosystems of the Aegean Islands have undergone processes of formation and geographical isolation differentiating them from the adjacent mainland, they have attracted many scientists. Although several papers describing the freshwater molluscs of these islands have been published, there is no such study about the Turkish islands of Gokceada and Bozcaada located in the northern Aegean Sea. This study describes the diversity of the freshwater mollusc fauna of Gokceada. Sampling of freshwater snails by kick-net and hand-collection was carried out throughout the island, covering diverse habitats including fountains, streams, and artificial ponds. The findings include the first records of Dreissena polymorpha and Pisidium subtruncatum from Gokceada and the invasive gastropod Physella acuta. Furthermore, we present descriptions of the anatomy and shells of four new species of freshwater snails: Pseudamnicola cirikorum sp. n., Pseudamnicola radeae sp. n., Grossuana kayrae sp. n., and Bythinella gokceadaensis sp. n. We compare these new species (except G. kayrae sp. n.) with previously described congeners from the Sporades, mainland Greece, and western Turkey. Because Grossuana had previously not been recorded from Turkey, G. kayrae is compared with Greek and Balkan (southwestern Thrace) Grossuana species.