Previous visual event-related potential (ERP) studies using prime–target pairs of word and pseudoword stimuli have reported a robust rhyming effect such that nonrhyming targets elicit a larger N450 than rhyming targets. However, results of similar studies using simpler linguistic stimuli—single letters—are equivocal. We used lowercase and uppercase letter pairs in a simple ERP prime–target rhyming paradigm to further investigate whether single letters could elicit the typical rhyming effect and, if so, whether the rhyming effect was sensitive to physical orthography (which differed between the case conditions). The typical N450 rhyming effect was observed in both the lowercase and uppercase letter pair conditions, with similar amplitude and latency between conditions. This pattern of results suggests that the N450 rhyming effect is not sensitive to physical (case) orthography and likely primarily indexes phonological processing related to the rhyme task.