The experiment reported here investigated the sensitivity of concreteness effects to orthographic neighborhood density and frequency in the visual lexical decision task. The concreteness effect was replicated with a sample of concrete and abstract words that were not matched for orthographic neighborhood features and in which concrete words turned out to have a higher neighborhood density than abstract words. No consistent effect of concreteness was found with a sample of concrete and abstract words matched for orthographic neighborhood density and frequency and having fewer neighbors and higher-frequency neighbors than the words of the first sample. Post hoc analyses of the results showed that orthographic neighborhood density was not a nuisance variable producing a spurious effect of concreteness but, instead, that the existence of higher-frequency neighbors constitutes a necessary condition for concreteness effects to appear in the lexical decision task. This finding is consistent with the hypothesis that semantic information is accessed and used to generate the responses in lexical decision when inhibition from orthographic forms delays the target word recognition.