Despite a history of reading or spelling difficulties, some adults attain age-appropriate spelling skills and succeed at university. We compared the spelling of 29 such high-functioning dyslexics with that of 28 typical students, matched on general spelling ability, and controlling for vocabulary and non-verbal intelligence. Participants wrote derived real and pseudo words, whose spelling relationship to their base forms was categorized as phonologically simple (aptaptly), orthographically simple (deceit-deceitful), phonologically complex (ash-ashen), or orthographically complex (plenty-plentiful). Dyslexic participants spelled all word and pseudoword categories more poorly than controls. Both groups spelled simple phonological words best. Dyslexics were particularly poor at spelling simple orthographic words, whose letter patterns and rules must likely be memorized. In contrast, dyslexics wrote more plausible spellings of orthographic than phonological pseudowords, but this might be an artefact of their more variable spelling attempts. These results suggest that high-functioning dyslexics make some use of phonological skills to spell familiar words, but they have difficulty in memorizing orthographic patterns, which makes it difficult to spell unfamiliar words consistently in the absence of sufficient phonological cues or orthographic rules.