Background: Previous research has shown that syllables are important units in visual word recognition in Spanish. If they are treated as real phonological units, then other related phonological features such as lexical stress (syllable prominence) may also play a role in this process. At times, lexical stress is the only difference between minimal pairs in Spanish (e.g., sábana 'sheet' vs sabana 'savannah'). These words are usually distinguished by an accent mark. This research examines whether lexical stress is used in visual word recognition and the role of the written accent mark in this process. Methods: In a lexical decision task, words with an irregular stress pattern according to generative phonological rules (e.g., "túnel" 'tunnel' or "mitin" 'meeting') were compared with regular words (e.g., "melón" 'melon' or "grifo" 'faucet'). Results: Irregular words without an accent mark ("mitin") were particularly difficult to recognise. However, irregulars that carried an accent mark were identified significantly more quickly and accurately. Conclusions: These findings are discussed as evidence that lexical stress may be an important cue in visual word recognition in Spanish, as suggested by previous research in the psycholinguistic and educational fields, and that models of visual word recognition should consider the impact of the accent mark in languages such as Spanish.