Abstract This paper describes and discusses certain characteristics of a case of developmental dyslexia, H. M., who was first examined at the age of six; his development of written and spoken language was kept under observation until he was eleven years of age, as he continued to complain of dyslexia and dysgraphia. In the written language, he had a difficulty of associating (kana) letters and symbols (numeric and Chinese characters) with their sound values (in the case of hiragana) and pronunciation (in the case of kanji and numbers). He finally learned to establish the needed associations but through an extra effort of using a keyword or object as a semantic reminder (a “conveyor or bridge,” as it were) to connect sound and its written representation (hiragana, kanji, or numeral). Even after he had acquired the sound-symbol relationships, he continued to make two specific types of errors when reading and writing hiragana and kanji: One is of phonemic type which pertains to errors in reading hiragana; the other is of semantic type which occurs when reading kanji. These types of errors, coupled with evidence from the literature reported by others, suggest that H.M. had in his CNS a weak association between the visual (i.e., configurative) aspect of symbols (in the case of hiragana) and their phonemic aspect (i.e., the phonetic values conventionally attached to or represented by them), on the one hand, and a good (i.e., intact) association between the visual aspect of symbols (in the case of kanji) and their semantic aspect (i.e., the meaning conventionally established with them), on the other. In contrast, he manifested a naming difficulty and a paraphasia in picture-naming tasks in the spoken language. Careful observations of his naming difficulties indicate that he made fewer errors in naming tasks when only a single (i.e., auditory-verbal) modality was involved than when two (i.e., visual and auditory-verbal) modalities participated in the tasks. These characteristics of his written and spoken language suggest a functional impairment of the association between visual information conveyed through the visual modality and auditory-verbal information transmitted through the auditory-verbal modality. It is further argued that, as a theoretical construct, the written and spoken language deficits of a developmental dyslexic resemble to a great extent the symptoms of alexia with agraphia in adult. Such being the case, the paper concludes that the studies of H.M.'s written and spoken language deficits have now made possible a cogent albeit partial explanation of the nature of impairment that underlies the long-disputed problems of the so-called language disorder syndrome.