The aim of the study was the evaluation of chromosomal aberrations, especially locus q11-q13 of chromosome 15 and polymorphisms in the g-aminobutyric acid receptor subunit B3 gene (GABRB3) and genetic aetiology of autistic disorder. We studied 20 probands (aged 4-27 years old) and their parents and siblings (73 persons). Following cytogenetic methods were used: conventional GTG-banding analysis, study of fra(X), fluorescence in situ hybridisation, with two specific probes: SNRPN and UBE3A/D15S10. Dinucletide (CA)n repeat polymorphism at the GABRB3 gene was analysed using PCR-STR method. Chromosomal analysis revealed paracentomere inversion--46, XX, inv(9)(p11q13) in 1 patient, but this is frequently found in population chromosomal variation. FISH didn't reveal abnormalities in 15q11-q13 region. ETDT analysis didn't reveal connection between autistic disorder and studied marker. Lack of anomalies in 15q11-q13 region may be related to small number of probands, heterogenity of studied group and small number of studied locus and markers. So conclusions should be related only to this studied group, and not to all autistic patients.