At the beginning of 1921 Klein leaves her in-laws in Rosenberg and moves to Berlin. Other psychoanalysts have also left Hungary due to the intensifying anti-Semitic climate, including Sándor Rádo, Alexander, Schott and Balint.

After a few weeks spent in a pension in  Grünewald, Klein moves to Cunostrasse, a drab and uninspiring area. She has Erich with her, now six years old. Melitta, aged 17, is finishing her studies in Budapest, and Hans, aged 14, is at boarding school.

Berlin is the most thriving psychoanalytic forum of the day. The first psychoanalytic clinic was opened in 1920, and training is becoming increasingly rigorous and structured, with training analysis and required supervision.

In February Klein delivers her first psychoanalytic paper to the Berlin Society on 'Felix’s' learning inhibitions. It is possible, though highly uncertain, that 'Felix' is in fact her son Hans.

Klein publishes an expanded version of her 1919 paper on Erich, her son now disguised as 'Fritz.'