Södermalm is a city district area (Swedish: stadsdelsområde, often referred to as a borough) in centralStockholm, created January 1, 2007, through the merging of the boroughs of Maria-Gamla Stan and Katarina-Sofia. It covers the island of Södermalm and some neighboring districts.
The two former boroughs made up the eastern and western half of the island of Södermalm. The Maria-Gamla Stan also included the island districts of Gamla Stan, Långholmen, Reimersholme, Riddarholmen and Årsta holmar; Katarina-Sofia included the district Södra Hammarbyhamnen south of Södermalm. All these districts are now parts of the new Södermalm borough.
Maria-Gamla Stan was the result of a previous merging between the original borough with the same name, and the former borough of Hornstull, in 1999.
Södermalm borough has a population of around 110,000, making it the most populated borough of Stockholm. The area Hammarby Sjöstad is located in the Södermalm borough.