The aim of this paper is to compare two English language film adaptations (by Steven Soderbergh and Ari Folman) with each other and with the books they are based on. Stanisław Lem’s novels - The Futurological Congress and Solaris - were translated into English and the directors of the films mentioned above were able to work with them. However, while one translation was appreciated by many, including the author of the original, the other one did not get much credit and features many inaccuracies, which will be presented below. The question of how much the quality of translation influences the intersemiotic translation, which adaptation is believed to be, will be examined in the paper. As, according to translation scholars, preliminary interpretation is vital for any translations, it seems justified to state that without being able to refer to the author’s original thoughts the film-makers cannot produce a good adaptation. This will be revised on the basis of comparing examples from the books and films. The analysis will be drawn on an account of translation and film adaptation theories together with the outlining of cultural background for each work.