Semantic errors are a common type of slip of the tongue for normal speakers; they are also considered to be the hallmark of progressive diseases that affect semantic memory such as Alzheimer's Disease (AD) and semantic dementia. In unimpaired speakers, semantic errors have been shown to be affected by syntactic variables. For example, Marx (1999) has shown that speakers of a gendered language such as German tend to substitute a target with another word that shares the same grammatical gender with the target more often than chance would predict. This finding suggests that errors occur at a level at which lexical information about the target is activated and retrieved. Here, we assess whether such an effect of syntactic variables (gender) also holds in experimental tasks designed to induce errors in unimpaired speakers of Italian (another gendered language) and whether this effect can also be observed in the semantic errors produced in the same task by AD patients. We found that for the unimpaired speakers, the gender of the target word constrained the error committed, while this was not the case for the AD patients. We take this finding to suggest a different locus for the errors in the two populations: while the semantic errors by the unimpaired speakers occur because of mis-selection of a lexical entry due to lexical competition among semantically similar words, the errors by the AD patients occur because of insufficient activation of lexical representations.