Developmental anomalies resulting in a single eye (cyclopia) or fusion of the eyes (synophthalmia) are rare. Examples of unilateral synophthalmia-in which there are 1 normal and 2 fused eyes from 3 anlagen in 2 orbits, 1 lateral proboscis, and 3 optic nerves-are even more rare. Herein, I report a unique fetus with unilateral synophthalmia that was not associated with a lateral proboscis but instead had an extra cerebral hemisphere. I postulate that the unilateral synophthalmia, accessory cerebral hemisphere, and minor structural abnormalities in the skull base were the result of failure in separating a monozygous twin, a situation similar to that postulated as the cause of fetus in fetu.