When two orthographically similar words are displayed using rapid serial visual presentation (RSVP), the repeated letters in the second critical word (W2) are not detected, leading to a deficit in reporting this word known as repetition blindness (RB). In Turkish, letters containing diacritic markings (e. g., s x, o) are considered separate letters, yet are visually highly similar to their non-diacritic analogues (s, o). Two experiments used the phenomenon of RB to investigate whether diacritic letters are represented as more similar to their non-diacritic analogues than are two unrelated letters. In Experiment 1, substantially more RB was found for words differing in just a diacritic (isim-isim) compared to orthographic neighbours (words differing in a visually non-similar letter, such as ilim-isim). In Experiment 2, the amount of RB for identical words (isim-isim) was comparable to words that differed by a single diacritic marking (isim-isim). We conclude that diacritic letters are mentally represented as variants of their non-diacritic analogue. Letter/word recognition researchers may be interested in pursuing these findings using standard techniques such as backward masking and orthographic priming.