The present study exploited the neuropsychological condition of patient DE, presenting with a unique combination of left neglect dyslexia (ND) and Deep Dyslexia (DD), to investigate how prefixed words are processed and represented by the human cognitive system. Semantic transparency and stem boundedness are lexical factors considered to characterize prefixed words. Symptoms of both ND and DD are influenced by the mental organization of complex words. In DD reading is possible only via the lexicon: errors of morphological nature derive from the fact that complex words may be stored as decomposed in root and affixes. In ND the left side of words is ignored: morphological boundaries, rather than merely spatial factors have been shown to modulate reading. By observing how the two syndromes interact in affecting the reading performance of patient DE, information on the processing and storage of different prefixed words can be obtained. Thus, a set of prefixed and pseudo-prefixed stimuli was administered to patient DE. Prefixed words were differently selected considering factors of semantic transparency and stem boundedness. The two syndromes resulted sensitive to the structure of prefixed words: the vast majority of left errors respected morphological boundaries; moreover, words error rates distributed unequally depending on factors like semantic transparency and stem boundedness. These results provide striking evidence that attention to written material is modulated by lexical information. DD would diminish the likelihood of committing errors on words whose internal representations are likely to be stored as unitary. The left side of these words resulted less sensitive to the effects of ND.