This prospective, longitudinal, study charted the developmental profiles of young children with Autism Spectrum Disorders (ASD) identified through routine developmental surveillance. 109 children with Autistic Disorder (AD), 'broader' ASD, and developmental and/or language delays (DD/LD) were assessed using the Mullen Scales of Early Learning (MSEL) at 12-months (n = 10 assessments), 18-months (n = 45 assessments), and 24-months (n = 99 assessments). The children with AD performed most poorly, overall, than the ASD and DD/LD groups on the MSEL. Furthermore, the children with AD/ASD displayed an uneven cognitive profile, with poorer performance on verbal (particularly receptive language) relative to nonverbal skills. There was also evidence of developmental slowing in verbal skills from 18- to 24-months for children on the spectrum, especially those with AD. Given that the poor receptive, relative to expressive, language profile emerges very early in life for children with AD/ASD, this cognitive profile may serve as an additional red flag to social attention and communication deficits. Receptive language should therefore be stringently monitored in any developmental surveillance program for autism spectrum disorders in the second year of life.