Achondrogenesis Type II (ACG2) is a lethal skeletal disorder caused by a dominant mutation in the type II collagen gene (COL2A1). Familial cases have been reported, suggesting both germline and somatic mosaicism. We report on two pregnancies from the same couple with gross, radiologic, and microscopic findings of ACG2. Molecular analysis of the second infant demonstrated heterozygosity for a c.2303G > A transition (p.Gly768Asp) in exon 33 of the COL2A1 gene. Although this mutation could not be proven by molecular studies in the first infant, identical findings in two affected pregnancies support germline mosaicism as the cause of ACG2 in this family. © 2010 Wiley-Liss, Inc.