Danish dancer and artistic director of the Royal Danish Ballet. He was known as an outstanding interpreter of roles in a variety of choreographic styles.

Kronstam was trained as a dancer at the Royal Danish Ballet School and joined the Royal Danish Ballet in 1952. He was one of the first Danish male dancers to be trained by the Russian teacher Vera Volkova (Volkova, Vera) after she emigrated to Denmark. In one of Kronstam's early performances, he created the role of Romeo in Frederick Ashton (Ashton, Sir Frederick)'s successful Romeo and Juliet (1955). This was a particular honour for the young dancer because it was the first full-length Romeo and Juliet to be produced outside of the Soviet Union. During his career, Kronstam performed some 130 roles, including all the great parts in the ballets of the 19th-century Danish choreographer August Bournonville (Bournonville, August). A danseur noble, he was especially known for his performances as James in La Sylphide and Albrecht in Giselle. He was also considered an outstanding dancer in the classical repertory, and, as he grew older, he moved into character roles, notably Lord Capulet in Romeo and Juliet and Peppo in Napoli. Other acclaimed performances include Jean in Miss Julie, Nilas in Moon Reindeer, and the title role in Cyrano de Bergerac.

In 1965 Kronstam became director of the Royal Danish Ballet, and in 1978 he succeeded Flemming Flindt to become artistic director. The following year he organized the Bournonville festival to commemorate the 100th anniversary of the choreographer's death. The weeklong festival, which attracted an international audience, presented all of Bournonville's complete surviving ballets. After resigning as artistic director in 1985, Kronstam continued to be active in the Royal Danish Ballet, teaching and producing. He was also director of the Royal Danish Ballet School.