In this study, the authors analyzed 2,056 spelling errors produced by 130 young adults (65 with dyslexia, 65 typically achieving), which came from two sources: a standardized spelling test and an impromptu essay-writing task. Students with dyslexia exhibited higher spelling error rates across both tasks. To characterize the inaccurate spelling attempts of both groups, the authors conducted linguistic and item-level analyses. Among unconstrained errors (essay), students with dyslexia had more difficulty than their typically achieving peers with familiar, low-level items (indexed by word frequency and number of syllables). Among constrained errors (spelling dictation), group differences in phonetic plausibility, morphological awareness, and visual accuracy varied by item. These analyses were telling on low-frequency items for which the groups obtained similar (dichotomous) accuracy rates. The authors suggest that diagnosticians and educators employ error analysis to obtain critical information not typically reflected in the standard scores used to make learning disability identification decisions. (Contains 8 tables and 2 notes.)