Connatal thalamic calcifications in apparently uneventful pregnancies have been described in various case reports and in a single report in two sibs. On the other hand, this lesion is known to occur after a hypoxic-ischemic accident in the immature brain. In the present report infantile encephalopathy with symmetrical thalamic calcifications is observed in one sib of a monozygous twin pair. This observation adds to the evidence that the condition is acquired, most probably on the basis of hypoxia-ischemia, and provides strong evidence against autosomal-recessive inheritance.