In the early 1980s, Prochnow was in a relationship with Austrian Actress Antonia Reininghaus who fatally poisoned their Common seven-year-old daughter Johanna in 1987. In 1982, he married actor Jürgen Goslar′s daughter Isabel Goslar, with whom he has two children: a daughter, Mona, and a son, Roman. The couple divorced in 1997. From 2004 to 2014 he was married to Birgit Stein, a German Screenwriter and Actress. Since 2015, he has been married to Actress Verena Wengler.