We report the case of ET, a 7-year-old child with a severe developmental letter-processing impairment. Detailed assessment revealed multiple impairments of the letter-processing system affecting abstract visual letter representation, semantics, and connections between the phonological processing modules and the orthographic buffer. Treatment methods focused on letter sounding through development of abstract visual representation and semantic representation of letters. Treatment resulted in dramatic and enduring improvements in cross-case matching, letter/number categorization, and letter sounding. Cognitive neuropsychological reading research has largely focused on word processing, with a relative neglect of single-letter processing. The current study investigated letter processing in greater detail than has been usual and outlines a broad theoretical framework for letter processing. ET's assessment and treatment data are used to support and question predictions from the framework. A number of theoretical implications are discussed with reference to ET's data and that of other reported cases of impaired single-letter processing. Finally, the paucity of investigation of letter processing in children is highlighted, particularly with regard to integrity of abstract letter representation in developmental dyslexia.