<p>CTNNB1 syndrome is a rare neurodevelopmental disorder caused by a likely pathogenic or pathogenic variant in the <i>CTNNB1</i> gene. A systematic review was conducted to examine previous research that provided CTNNB1 syndrome patients, specifically those that described intellectual quotient, motor development, language impairments, behavioural problems and features of autism. Databases examined were PubMed and Scopus. The inclusion criteria were (a) reported human patients diagnosed with CTNNB1 syndrome by a genetic test; (b) were related to cognition, intelligence quotient, motor development, language impairment, behavioural problems or features of autism; (c) did not have another genetic diagnosis and (d) were written in Spanish or English. A total of 42 studies were included. Overall, the symptomatology described was very heterogeneous with varying degrees of impairment among patients. However, individuals reached most significant developmental milestones later than expected and with different degrees of impairment. The use of standardised methodology to assess cognitive and behavioural domains was scarce in most studies, and the vast majority did not include a specific assessment protocol based on the symptomatology of CTNNB1 syndrome individuals. In addition, only two adult patients were described in depth, which implies that there are many unknowns about the progression of the syndrome later in life. Therefore, future research should focus on increasing the sample assessed and count with a standardised protocol in order to characterise the cognitive and behavioural phenotype of CTNNB1 syndrome.</p>