Much of the available literature on individuals with trisomy 9 mosaicism focuses on reports concerning results of prenatal testing or fetal autopsy with limited reports of long-term survivors. Data from the Tracking Rare Incidence Syndromes (TRIS) project offer the largest series to date examining the presenting physical characteristics and medical conditions at birth for 14 individuals. Results indicated the presence of low set ears and microcephaly for some children in the sample. Cardiac anomalies were reported along with feeding and respiratory difficulties in the immediate postnatal period. In addition, developmental status data indicated a wide range in functioning level with examples of demonstrated skills provided. Implications for professionals caring for patients with trisomy 9 mosaicism are offered. © 2011 Wiley-Liss, Inc.