Purpose: Cowden syndrome (CS) is an autosomal dominant disease related to germline PTEN variants and is characterised by multiple hamartomas, increased risk of cancers and frequent brain alteration. Since the behaviour of patients with CS sometimes appears to be inappropriate, we analysed their neuropsychological functioning. Methods: This monocentric study was conducted between July 2018 and February 2020. A standardised neuropsychological assessment, including an evaluation of social cognition, executive functions, language and dexterity, as well as a cerebral MRI were systematically proposed to all patients with CS. Moreover, PTEN variants were identified. Results: Fifteen patients from 13 families were included, with six non-sense (40%), three missense (20%), five frameshift (33.3%) and one splice site (6.6%) variant types. Twelve patients (80%) had altered social cognition: 10 patients had an abnormal modified Faux-Pas score and 5 had Ekman's facial emotions recognition impairment. Nearly all patients (93%) had impaired dexterity. Cerebral MRI showed various cerebellar anomalies in seven patients (46.7%). Conclusion: Altered social cognition and impaired fine dexterity are frequently associated with CS. Further studies are needed to confirm these results and to determine whether dexterity impairment is due to the effect of germline PTEN variants in the cerebellum.