The X and Y chromosomes are responsible for the determination and differentiation of the gonads, and their numerical and structural abnormalities may cause the abnormal development of secondary sex characteristics. The presence of abnormalities concerning X chromosome can also contribute to many genetically heterogeneous diseases associated with cognitive impairment and intellectual disability. This study shows the effect of aberrations of the maternal X chromosome on the abnormal development of the child. Ten women aged 26 to 40 years were consulted in genetic counselling clinic and subsequently subjected to cytogenetic and molecular tests due to abnormal psychomotor development of their children, in whom structural aberrations of the X chromosome had been detected. Two women were diagnosed with changes in karyotype: 46,X,der(X)t(X;Y)(p22.3;q11.2) in one and 46,X,inv(X)(p21.2q13). Five women were diagnosed with microduplications in the short arm of the X chromosome; dupXp22.31 in one, and in four women dupXp22.33. The remaining three women were diagnosed with duplication in the long arm of the X chromosome; dupXq25 in one and dupXq26.3 in two women. Genetic analysis of the X chromosome, based on cytogenetic and molecular methods of the highest available resolution, is extremely important in women with reproductive failure. These methods allow establishing accurately the breakpoints and rearrangements in chromosomes, and assessment of the copy number variation (CNV) can explain phenotypic variability with apparently similar aberrations. A more precise characterization of the alterations is necessary for the correct genetic diagnosis, as well as determination of the carrier status and genetic risk in family members.