Dandy-Walker syndrome (DWS), or Dandy-Walker complex, is a congenital brain malformation of the posterior fossa, typically resulting in developmental delay and cognitive disability. The co-occurrence of Down syndrome (DS) and DWS is relatively uncommon; thus, its impact on developmental outcomes has not been fully elucidated. Herein, we report a case of a 37-month-old child with DS and DWS, who is functioning at the following age-equivalent: gross motor at a 9-mo level, fine motor 6 mo, expressive language 14 mo, receptive language 9 mo. As such, it is important to determine how the DWS influences developmental outcomes, and appreciate the importance of early interventional therapy.