We report the occurrence of symmetrical thalamic calcifications (STC) in one of a pair of monozygotic twins born at term without evidence of pre- or peri-natal asphyxia. STC is known to be an extremely rare condition in infants. Judging from the few cases reported in the literature, the clinical presentation is very severe: low Apgar score, no spontaneous movements, spasticity or marked hypotonia, impaired suck and swallow, facial diplegia. The prognosis is also very poor. The etiology is still a matter of debate: genetic, infectious, toxic or hypoxic-ischemic insults have been hypothesized. In our case, the presence of the lesion in one of a pair of monozygotic twins would rule out any genetic origin, nor was there any evidence of toxic or infectious disease. The only potential risk factor for fetal damage was hypoxic-ischemic insult related to the twin pregnancy.