OBJECTIVE: To determine the long-term outcome of pregnancies prenatally diagnosed with trisomy 16 and identify variables associated with the outcome. METHODS: We reviewed all published and our unpublished data from trisomy 16 pregnancies for which outcomes were available for children of greater than 1 year of age. RESULTS: Nineteen cases were diagnosed with trisomy 16 on chorionic villus sampling (CVS) and 17 cases at amniocentesis. Age at last follow-up ranges from 1 to 13 years. Among the CVS group, four out of five patients, with a birth weight and/or length below -2 SD and postnatal growth information, showed catch-up growth (80%). Among the amniotic fluid (AF) group, the birth weight was available in 13 cases. Eleven of the 13 cases had a birth weight less than -2 SD. In eight cases, the length was also below -2 SD (length data unavailable in one case). Nine out of ten cases (90%) and seven out of eight (87.5%) showed catch-up growth for weight and length, respectively. In terms of development, no cases of CVS mosaicism had global developmental delay. One child had a history of delay in speech development. Among the AF-detected cases, 4/17 cases had global developmental delay. All four children with global developmental delay had more than one major malformation compared to 6 out of 32 children in the group with normal development (p = 0.004). The finding of uniparental disomy (UPD) was not associated with developmental delay. CONCLUSIONS: The majority of prenatally diagnosed trisomy 16 mosaic cases have a good postnatal outcome. However, the finding of mosaicism on AF and the presence of major congenital anomalies are associated with an increased risk of developmental delay. Copyright 2006 John Wiley & Sons, Ltd.