A leiomyoma is a benign tumor originating from nonstriated muscle that is typically found in the uterus. Intravenous leiomyomatosis is a rare form found within the veins, usually associated with uterine fibroids, and tends to recur. These masses can spread from the uterus throughout the venous system. A rare case involving a subendothelial leiomyoma found in an umbilical cord artery is presented in this article. A 21-year-old patient presented with symptoms of preterm labor, which resulted in the premature birth of a female below the 10 th percentile for 24-wk gestational age. The newborn died three days later, and microscopic analysis of the umbilical cord revealed occlusion of the artery by nodular structures. The antepartum diagnosis of intravascular leiomyoma was identified by immunohistochemistry showing that approximately 70% of all tumor cells were diffusely positive for smooth muscle markers, including desmin and smooth muscle actin. These findings indicate the possibility of a pathologic association between the umbilical cord leiomyoma, restriction of fetal growth and preterm delivery due to impaired circulation of blood in the umbilical cord. A leiomyoma is a benign tumor originating from nonstriated muscle that typically typically found in the uterus. Intravenous leiomyomatosis is a rare form found within the veins, usually associated with uterine fibroids, and tends to recur. These masses can spread from the uterus throughout the venous system. A rare case involving a subendothelial leiomyoma found in an umbilical cord artery is presented in this article. A 21-year-old patient presented with symptoms of preterm labor, which resulted in the premature birth of a female below the 10 th percentile for The newborn died three days later, and microscopic analysis of the umbilical cord revealed occlusion of the artery by nodular structures. The antepartum diagnosis of intravascular leiomyoma was identified by immunohistochemistry showing that approximately 70% of all tumor cells were diffusely positive for smooth muscle markers, including desmin and smooth muscle actin. These findings indicate the possibility of a pathologic association between the umbilical cord leiomyoma, restriction of fetal growth and preterm delivery due to impaired circulation of blood in the umbilical cord.