Sampaio's first wife was a physician named Karin Schmidt Dias, daughter of António Jorge Dias (Porto, 31 July 1907 – Lisbon, 5 February 1973) and Margot Schmidt. The couple had no issue and later divorced. He later married Maria José Rodrigues Ritta (b. Lisbon, 19 December 1941), daughter of José António Ritta and wife Maria José Rodrigues Xavier and sister of Maria Ermelinda and José António. Sampaio and his second wife had two children: Vera Ritta de Sampaio (b. 1977) and André Ritta de Sampaio (b. 1981).