After the German capitulation, Leros will remain for a while under British administration. On 31 December 1947 in Platanos, the English flag will be replaced by the Greek.
The incorporation of the island to Greece will be officially celebrated on 7 March 1948.
During the postwar years, Greek governments have used many of the buildings on the island for several reasons.
In 1949, the so-called "Royal Schools" were established in a section of abandoned Italian barracks. The "Royal Schools", was a center of national education of young rebels and children, who for several reasons were found in the civil war without family.
Apart from learning some art for future professional employment, there has been an effort for ideological and political adjustment in the name of the then official doctrine, Anticommunism. About 16,000 young people passed from the “Royal Schools" of Leros, living in conditions of discipline, while approximately 200 people from the local population were working as instructors in various arts and for the schools maintenance. Their operation lasted, with dwindling course until December 1964 when the last students were graduated.
According to Royal Decree of 18/03/1957, the ‘Psychopaths Colony’ is established in Leros and is being accommodated in buildings of the Italian Naval Base at location "Corner" in Lakki. Later, due to the increasing influx of patients the buildings of the former Italian Air Base in area ‘Lepida’ will be used as well.
In1965 the Institution of the ‘Psychopaths Colony’ is being amended, is renamed as "Leros Psychiatric Hospital 'and provides 2,650 beds and 625 employees.
During the dictatorship, from April 1967 until July 1974, Leros becomes a place of concentration camps of political prisoners, rivals of the dictatorship, mainly leftists. From September 1967, the political prisoners in the camps of St. George and Partheni, but also in the displacements at Agia Marina, will approach the 1/3 of the total number of political prisoners of the dictatorship (7900).