Thanatophoric dysplasia is the most common lethal form of skeletal dysplasia with typical ultrasound findings that can be identified before the 20th week of gestation. We describe the prenatal ultrasound findings in a twin pregnancy. Both presented macrocephaly, prominent forehead, flat nasal bridge, short, thick ribs and hypoplastic narrow thorax, severe shortening limbs, flat vertebrae, mild polyhydramnios and decreased fetal mobility. Thanatophoric dysplasia type I was suspected. It was explained to the couple the lethal nature of the disorder but they decided to continue their pregnancy. At 34 weeks the mother presented data from severe preeclampsia and was decided to perform cesarean section obtaining two male infants with poor respiratory effort and generalized cyanosis. Usual maneuvers for newborn care were omitted and both died within minutes after birth. The physical examination shows macrocranium, disproportion skull/face, prominent forehead, midface hypoplasia, flat bridge, tongue protrusion, short neck, narrow thorax, prominent abdomen, micromelia and bilateral trident sign. We reviewed the existing criteria for antenatal diagnosis of skeletal dysplasias based on the use of tools such as ultrasound in third and fourth dimension, as the detection and early diagnosis improves pregnancy counseling the couple about the outcome of the fetus.