Description of diagnosis of 45,X/46,XY ovotesticular DSD.Case report.Department of Medical Genetics, KZ a.s., Masaryk Hospital, Ústí nad Labem.45,X/46,XY ovotesticular DSD is a diagnosis, which in this case was detected by chromosomal examination was performed, in which the child showed karyotype 45,X[2]/46,XY[8] - a pathological male karyotype correlated with the syndrome 45,X/46,XY ovotesticular DSD (disorder of sexual development). At the same time, a variant of chromosome 10:45,X,inv(10) (p11q21.2)/46,XY,inv(10)(p11q21.2) was detected.The phenotype of patients with mosaic karyotype 45,X/46,XY ranges in a wide range from the female phenotype with classical Turner syndrome, through individuals with ambiguous genitals to normal but infertile men. Thus, both Turners syndrome and virilization can be expected. Gonads are usually dysgenetic with insufficiently differentiated testicular tissue, which can occur in both gonads (mixed gonadal dysgenesis) or only in one (asymmetric gonadal dysgenesis). With this type of gonadal dysgenesis, there is a risk of gonadoblastoma or other tumors.