This work analysed the comprehension of three types of idioms of the V+NP form (e.g., bite the dust) in seven patients with aphasia and two patients with probable Alzheimer's disease, frontal variant. The aphasic patients included in the study had a severe semantic disorder or a mild semantic deficit, or only a lexical disturbance. Participants with dementia showed a moderate deterioration in their executive functions and no impairment in their psycholinguistic performance. In this study, we used an idiom–word matching task, administered in two versions. The results indicate dissimilar performance patterns, according to patients' neuropsychological impairment. In particular, patients with a severe semantic disorder showed a poor understanding of the figurative meanings of idioms, especially if those idioms were not fully transparent or opaque. Participants with a mild semantic deficit accessed the non-literal meanings of the idioms showing less difficulty in the case of certain idiomatic expressions. Patients with executive function deficit showed a double interference effect, and although they could activate the figurative and literal meanings of idioms according to the context in which they were presented, it was difficult for them to inhibit those meanings whenever necessary and activate the alternative meaning. This effect was more pronounced the less transparent the idiom was.