OBJECTIVES: The goal was to examine the incidence of ASD as well as prenatal, perinatal and postnatal risk factors, to analyze the clinical characteristics, phenotype, comorbidities and genetic background of ASD. STUDY DESIGN: A cross-sectional study with historical data. PARTICIPANTS AND METHODS: The research was conducted in the Outpatient Clinic for Genetics and Metabolism of the Clinic of Pediatrics, University Hospital Center Osijek. The examinees were 172 children who first visited the Outpatient Clinic between January 1st, 2011 and December 31st, 2021. Data were collected from medical documentation: personal and family history of the child, general data on parents and siblings, pregnancy, childbirth and pre-, peri- and postnatal risk factors, clinical characteristics and findings of other necessary medical examinations. RESULTS: There is a significantly higher percentage of male examinees (78 %). Dominant prenatal risk factors include parental age of ≥ 35 years, illnesses and medication taken during the pregnancy, with special emphasis on drugs that affect the CNS. Important perinatal risk factors cover the Apgar score of ≤ 7, birth weight of ≤ 2500 grams and signs of fetal distress at birth. While motor development was mostly in order, social and speech development show significant divergence. Stereotypical and ritual behavior was present in most children (72 %). Other examinations, including audiological, neurological and genetic testing, were in most cases normal. Genotype and phenotype were also normal in a high percentage. The most common comorbidities are hyperactivity, allergies and epilepsy. CONCLUSION: ASD is significantly more common in male children and children with positive prenatal, perinatal and postnatal risk factors with a sizeable influence of genetic and epigenetic factors