Since Kraepelin times, it is considered that the delusional disorder (DD) does not imply a cognitive deficit, unlike the paranoid schizophrenia (PS). However, empirical evidence is very limited.

To compare the neurocognitive functioning differences among healthy controls (HC), DD and PS patients.

Neurocognitive functioning was evaluated in 51 healthy controls, 69 DD patients and 41 PS patients (according to the SCID-I) using an extensive neuropsychological battery which evaluate five domains (attention, working memory, verbal memory, executive function and social cognition). Was performed multivariate analysis of covariance (ANCOVA) to compare differences in neuropsychological performance between the three groups. The potential confusion factors were controlled, like the socio-demographic characteristics, premorbid IQ (“National Adult Reading Test”), depressive symptoms (“Beck Depression Inventory”) and the positive and negative psychotic symptoms (“Positive and Negative Syndrome Scale”).

DD patients showed a considerably worse neurocognitive functioning than healthy controls regarding to attention, verbal memory, executive functions and social cognition; while DD patients compared to PS only present a better neurocognitive performance in attention.

DD patients shown that neurocognitive deficit is relevant, unlike what it is considered since Kraepelin up to date, as shown in the DSM-IV-TR and the CIE-10.