The first chapters of this thesis describe the process of collecting mispronounced words in English, first by searching through various sources including course books, didactic manuals and teachers' books; and second by attending English lessons at various schools and listening to Czech students' production of English. The collected data were classified according to the cause of observed mispronunciations. The established categories were analysed and commented from the phonetic point of view. The practical part further contains a small-scale research carried out among university students of the English language in which their reading was recorded and evaluated in relation to the examined phenomenon. Key words commonly mispronounced words, Czech native speakers, stress placement, silent letters