Trisomy 3 mosaicism in live birth is exceedingly rare. In this study, we report a 5-year-old boy with trisomy 3 mosaicism who exhibits skeletal anomalies, atypical form of ectodermal dysplasias, refractory diarrhea, and normal intelligence. Fluorescence in situ hybridization and microsatellite marker analyses confirmed the existence of trisomy 3 mosaicism and suggested that the parental origin of the additional chromosome 3 in the trisomic cells was maternal. This report further delineated the trisomy 3 mosaicism in live births. The authors propose that both common phenotypes and phenotypic diversity exist on cases with trisomy 3 mosaicism. © 2016 Wiley Periodicals, Inc.