The great Dr. Pfeiffer plays the little Primaner Pfeiffer. As the successful playwright Dr. Hans Pfeiffer, he is planning a play about school. In order to gather material, he takes the place of his brother, who is a primary school pupil. The seasoned doctor finds pleasure in the craziest of pranks, while his brother tries to fill the role of theater man in the big city. And then love intervenes for both of them.
| Actor | Role |
|---|---|
 Heinz RühmannDr. Hans Pfeiffer/ Erich Pfeiffer | Dr. Hans Pfeiffer/ Erich Pfeiffer |
 Rudolf PlatteTanzlehrer | Tanzlehrer |
 Ellen FrankMarion Eisenhut | Marion Eisenhut |
 Jakob TiedtkeRektor Knauer | Rektor Knauer |
 Oskar SimaProfessor Crey | Professor Crey |
| IInge ConradiIlse Bundschuh | Ilse Bundschuh |
 Annemarie SörensenEva Knauer | Eva Knauer |
| EElse BötticherFrau Knauer | Frau Knauer |
| EErwin van RoyBürglein, Regisseur | Bürglein, Regisseur |
| FFranz WeberNot listed | Not listed |
 Karl PlatenNot listed | Not listed |
| MMaria SeidlerNot listed | Not listed |
| WWalter SteinwegNot listed | Not listed |
| AAnita MeyNot listed | Not listed |