Issels opened his Ringberg Clinic in Bavaria in 1951. As the clinic achieved greater fame, patients from around the world began to seek his treatment. However, other doctors did not approve of his practice, specifically the Bavarian Medical Council, which charged Issels with fraud and manslaughter. After a four-year legal battle, Issels' convictions on all charges were overturned, and his clinic was re-licensed. Issels centers and clinics continue to treat cancer patients around the world, with all types and stages of cancer.