In the new classification of American Psychiatric Association – DSM-5 – a category of autistic spectrum disorders (ASD) was introduced, which replaced autistic disorder, Asperger syndrome, childhood disintegrative disorder and pervasive developmental disorder not otherwise specified. ASD are defined by two basic psychopathological dimensions: communication disturbances and stereotyped behaviors, and the diagnosis is complemented with the assessment of language development and intellectual level. In successive epidemiological studies conducted in 21 century the prevalence of ASD has been rising, and currently is estimated at 1% in general population. The lifetime psychiatric comorbidity is observed in majority of patients. The most common coexisting diagnoses comprise disorders of anxiety-affective spectrum, and in about 1/3 of patients attention deficit/ hyperactivity disorders could be diagnosed. Prodromal symptoms of ASD may emerge before 12 months of life, however reliability of diagnosis at such an early age is poor. Several screening instruments, based on the parental and/or healthcare professional assessments may be helpful in ASD detection. However, structured interviews and observation schedules remain the gold standard of diagnosis.