Rosenthal was born on 1 July 1932 in Jasina (modern day Yasina) in the Carpathian Mountains which was then the most easterly part of Czechoslovakia. In 1930 there were 1,471 Jews living in Jasina.
Rosenthal’s parents had a pre-arranged marriage through religious contacts with his mum originally born in Romania and only moving to Jasina after marrying Rosenthal’s dad, who was called Nachmann (b. 1891). The family was relatively wealthy with Nachmann being a merchant who owned a store and some land. Rosenthal had one brother who was four years older than him.