Unilateral aplasia of the nose is a rare congenital malformation. It is often associated with other malformations of the facial region, including abnormalities of the eye and lacrimal system, proboscis lateralis, and facial bone malformations. The authors present a case of heminasal aplasia in a 4-year-old boy who underwent surgery immediately after birth because of right-sided proboscis lateralis. A huge hemispheric tumefaction was occupying a large part of the right orbit, medial canthus, and frontonasal region of the face, causing lateroinferior protrusion of the eyeball. The right half of the external nose was aplastic. The patient was operated on by an external approach. The pathohistological findings from the top of tumefaction revealed cystic teratoma. The possible backgrounds for the onset of the tumefaction are discussed in two main directions: the cystic form of the regrowth of the remnants of inadequately excised proboscis lateralis and cystic teratoma of the ethmoidal sinus.