This essay attempts at an analysis of Janusz Korczak's Diary, written in the Warsaw ghetto in 1942. These records form an intimate diary and a consciously constructed literary piece, which was conceived as a polemic with 'Also sprach Zarathustra' by Friedrich Nietzsche. At all, it is a piece underspecified as to genre, perhaps intentionally so. Korczak applied in it several literary stratagems he had used before. Given this important observation, the reader can take a different look at certain controversial fragments of this Diary: the author's views on war and death, and, his apparently 'anti-Semitic' opinions. Besides, the Korczak account is confronted with other ghetto documents concerning its author, which were found at a later date.