The disorders of sex development (DSD) 46,XY may be caused by mutations in a number of genes involved in the gonadal differentiation. The XY sex inversion can be also due to disturbances at the level of mitogen-activated protein kinase (MAPK) kinase kinase 1 gene (MAP3K1) and MAPK-signaling pathway. During the last decade, the involvement of the MAPK pathway in the SRY gene up-regulation during the formation of male gonadal sex in mammals has been demonstrated. The role of MAPK-signaling pathway in the human sex determination is not fully understood. Probably, MAP3K1 and the MAPK-signaling pathway are one of the genetic pathways controlling normal development of human testis. So far, several families and sporadic cases of 46,XY DSD due to mutations in MAP3K1 gene have been reported in the literature. Clinical presentation of DSD in these patients varies from female phenotype with normal externalia to male phenotype with hypospadias. We describe rare cases of the DSD 46,XY (a family case of DSD in uterine sisters and a sporadic case) with mutations in the MAP3K1 gene that haven’t been previously described. The article also presents brief literature review on this pathology.