On 22 December 1974, Dietz won his debut for West Germany in a Euro 1976 qualifier against Malta in Malta. After his final game for his nation, on 19 May 1981, against Brazil in Stuttgart, he had been capped 53 times by Helmut Schön and Jupp Derwall. Participating also in the Euro 1976 and at the 1978 FIFA World Cup, Dietz was able to lift the 1980 UEFA European Football Championship trophy as the captain of the triumphant West German team.