The present study exploited the attentional deficit characterizing left neglect dyslexia (ND) to investigate how prefixed words are processed and represented by the human cognitive system. Spared morpho-lexical knowledge, in fact, has been shown to modulate the exploration of written material in ND, affecting the way left-sided errors manifest in patients’ reading performance. Semantic transparency and stem boundedness are lexical factors that may influence storage and processing of prefixed words in the mental lexicon. Thus, information on the lexical representation and processing of prefixed words can be obtained by observing how attention and lexical access interact in ND. Accordingly, the left side of prefixed words likely stored as whole units should result less easily affected by ND. In contrast, the left side of prefixed words likely processed as parsed should be more easily affected by the syndrome. A set of prefixed and pseudo-prefixed stimuli was thus administered to a patient affected by ND. Prefixed words were differently selected considering factors of semantic transparency and stem boundedness. ND resulted sensitive to the morphological structure of stimuli: the vast majority of left errors specifically affected prefixes. Additionally, ND was modulated by the lexical nature of stimuli: left-sided errors distributed unequally depending on factors like semantic transparency and stem boundedness. These results, by showing to what extent ND is sensitive to lexical factors engaged in higher-level processing of prefixed words, highlight the complex nature of this disturbance.