We present a case of triplets with intrauterine cytomegalovirus (CMV) infection, each of whom showed differential transmission, placental pathology, and postnatal outcome. The first- and second-born infants were both vigorous and asymptomatic at birth, although the first-, but not the second-born, triplet had a high copy number of CMV DNA in the peripheral blood (1.2 X 103 copy/mL). The third-born triplet suffered from symptomatic CMV infection with a high viral load (6.0 X 106 copy/mL). The triamniotic-trichorionic placentas were not fused to each other. The histopathologic analysis showed that CMV-positive cells were frequently found in the decidua, villi, and amnion of the third-born triplet’s placenta but were limited and scattered in the decidua or villi but not amnion of the other 2 placentas. The third-born triplet underwent ganciclovir therapy. None of the infants had physical or auditory problems at 4 years of age, whereas the third-born triplet had been diagnosed with an autistic disorder. This observation exemplifies the preventive roles of the individual placentas of triplets with regard to virus infection, thus suggesting that developing CMV disease largely depends on the placental function.