The purpose of this study is to describe clinical and laboratory data, as well as comorbid disorders in Greek children with autism spectrum disorders (ASD). Data were retrospectively collected for 222 children aged 1.5–9 years. The mean age at diagnosis was 43.7 ± 17.6 months. Significantly earlier diagnoses were noted in children with comorbid disorders (epilepsy, hearing deficits, genetic/metabolic disorders), mental retardation and a large head circumference (HC). Macrocephaly (HC ≥ 97th percentile) was found in 21.2% of children, genetic and metabolic disorders in 11.7% and 2.7% respectively and mental retardation in 23%. Patients with certain clinical features (i.e. syndromic) are earlier diagnosed. It is of ultimate importance to promptly identify all children with ASD, probably through the appliance of screening and surveillance programs in the Greek population.