Objectives: The analysis of karyotypes in fetuses with increased nuchal translucency (NT) and the assessment of correlations between NT thickness, presence of other fetal anomalies and the result of karyotype. Material and methods: The study was conducted among 121 singleton fetuses with increased NT thickness. In all fetuses the karyotype was assessed following amniocentesis. The results of karyotypes were analyzed in the whole studied group, as well as in specific subgroups of patients according to NT value: 1) increased NT, but not exceeding 3,5mm, 2) 3,5-4,4mm, 3) 4,5-5,4mm, 4) 5,5-6,4mm, and 5) ≥6,5mm. Results: Abnormal results of the karyotype were found in 41 out of 121 fetuses (33,9%). The most common aberration was trisomy 21. A percentage of abnormal fetal karyotypes increased with the degree of NT thickening and was 15,9% in fetuses with increased NT which did not exceed 3,5 mm and 54,5% in fetuses with NT ≥6,5 mm. The abnormal karyotype was diagnosed in 54,5% of fetuses with increased NT and other abnormalities found in ultrasound. Conclusions: 1. Around 65% of the fetuses with an increased NT have normal karyotype. 2. A percentage of abnormal karyotypes in fetuses increases with the degree of NT thickening. 3. An ultrasound finding of an increased NT and other abnormalities in a fetus is associated with higher risk of chromosomal aberrations in comparison to cases when there is only an increased nuchal translucency.