BackgroundClassical galactosemia (CG) is a rare inherited metabolic disorder associated with long-term neurodevelopmental, language, cognitive and psychosocial difficulties. Social-communication problems may overlap clinically with autism spectrum disorder (ASD), but paediatric data based on standardised ASD assessment remain limited.MethodsThe study included 50 children and adolescents aged 6–17 years with confirmed classical galactosemia. Intellectual functioning was assessed using the Stanford–Binet Intelligence Scales, Fifth Edition. Autism spectrum disorder (ASD) symptoms were evaluated using the Mini International Neuropsychiatric Interview for Children and Adolescents (MINI-KID), Autism Spectrum Rating Scales (ASRS, parent version), Autism Diagnostic Observation Schedule, Second Edition (ADOS-2), as well as comprehensive clinical assessment by a child and adolescent psychiatrist.ResultsA clinical diagnosis of ASD was established in 36% of participants. Results indicating ASD symptoms were obtained in 56% of children using MINI-KID, 48% using ADOS-2, and 30% based on overall ASRS scores. Statistically significant moderate negative correlations were found between IQ and ASD symptom severity, particularly in social communication, social-emotional reciprocity, and attention domains. Selected long-term disease-related manifestations (white matter abnormalities and osteopenia/osteoporosis) were more frequent in children with ASD symptoms identified by MINI-KID.ConclusionsChildren and adolescents with classical galactosemia in this clinical cohort frequently presented ASD-related social-communication difficulties, and a substantial proportion met criteria for a clinical ASD diagnosis.