Recent collections of isopods in Alboran Island and Algeria included several specimens of the species Stenosoma stephenseni sp. n. This is the fourteenth species described in the genus Stenosoma Leach, 1814. Examination of two specimens collected during the Danish oceanographic cruises of the Thor (1908–10) close to the Galite Islands, and identified as S. acuminatum Leach, 1814, revealed that both belong to S. stephenseni sp. n. In light of these findings, the Mediterranean records of S. acuminatum are revised, and it is proposed that S. acuminatum is a strictly Atlantic species. An updated diagnosis for the genus Stenosoma is given, together with a key for the identification of its species. The nomenclatural status of the name Synisoma Collinge, 1917 is addressed, and although it is in prevailing usage, it is shown that Stenosoma Leach, 1814 is the valid name of the genus.