Objective: To determine the demographic and clinical characteristics of children followed up with the diagnosis of autism spectrum disorder (ASD) at a tertiary center in Southeeast Turkey. Methods: Children followed up with the diagnosis of ASD at a university hospital child psychiatry clinic between June 2016 and June 2021 were evaluated retrospectively for comorbidities, intellectual functioning and age at diagnosis. Results: In the preschool group, females displayed significantly more frequent cognitive developmental delay. Median age at diagnosis was 36 months (IQR= 22) regardless of gender. Approximately three-fourth (73.7%) of the cases had at least one psychiatric comorbid disorder while 22.8% had at least one medical diagnosis. Psychiatric comorbidity was found to be associated with later diagnosis. Conclusion: Although the age at first diagnosis in this study is relatively earlier than the studies in the literature, most of the children with ASD are still diagnosed very late. Psychiatric comorbidities may lead to later diagnosis due to overshadowing. Training of educational and primary healthcare workers on symptoms of ASD may enable earlier diagnosis.