This study examined the developmental profile of male infants with fragile X syndrome (FXS) and its divergence from typical development and development of infants at high risk for autism associated with familial recurrence (ASIBs). Participants included 174 boys ranging in age from 5 to 28 months. Cross-sectional profiles on the Mullen Scales of Early Learning indicated infants with FXS could be differentiated from typically developing infants and ASIBs by 6 months of age. Infants with FXS displayed a trend of lower developmental skills with increasing age that was unique from the typically developing and ASIB groups. Findings suggest infants with FXS present with more significant, pervasive and early emerging delays than previously reported with potentially etiologically distinct developmental profiles.