This experiment investigates whether the influence of spelling-to-sound correspondence on lexical decision may be due to the visual characteristics of irregular words rather than to irregularities in their phonological correspondence. Lexical decision times to three types of word were measured: words with both irregular orthography and spelling-to-sound correspondence (e.g., GHOUL, CHAOS), words with regular orthography but irregular spelling-to-sound correspondence (e.g., GROSS, LEVER), and words regular in both respects (e.g., SHACK, PLUG). Items were presented in upper- and lowercase in order to examine the influence of “word shape” on any irregularity effects obtained. The results showed that irregular words with regular orthographies were identified more slowly than regular words in both upper- and lowercase. Words that are both orthographically and phonologically irregular were identified much more slowly with lowercase presentation. However, with uppercase, the lexical decision time for these items did not differ significantly from those of regular words. These data indicate that previous demonstrations of the regularity effect in lexical decision were not due to the unusual visual characteristics of some of the words sampled. In addition, the data emphasize the role of word shape in word recognition and also suggest that words with unique orthographies may be processed differently from those whose orthography is similar to other words.