We report on a girl with trisomy 12 mosaicism diagnosed postnatally. She has been followed from 4 months of age for developmental delay, unilateral sensorineural hearing loss, intestinal malrotation, hemi-hyperplasia, pigmentary dysplasia, retinopathy, and a vascular ring. To our knowledge, there have been no reports of complete trisomy 12 in the literature. However there have been a few reports describing the phenotype of individuals with trisomy 12 mosaicism. This case report is a description of the eighth liveborn individual diagnosed postnatally with this condition. © 2012 Wiley Periodicals, Inc.