This study examined the incidence of extreme sensory modulation behaviors in toddlers with autism spectrum disorders (ASD) and investigated the consistency of sensory information across measures. Parent report of sensory behaviors in 101 toddlers with ASD was compared with 100 toddlers who were typically developing matched on chronological age and 99 additional infants or toddlers matched on mental age. Measures included the Infant/Toddler Sensory Profile, Infant–Toddler Social Emotional Assessment, Autism Diagnostic Interview–Revised, and Autism Diagnostic Observation Schedule–Generic. Toddlers with ASD were most distinct from typically developing groups in their high frequency of underresponsiveness and avoiding behaviors and their low frequency of seeking. Within the toddlers with ASD, there were significant associations across sensory parent report measures, but parent report was not correlated with clinical observation. Findings point to the early onset of an extreme sensory profile in ASD. Occupational therapists need to assess multiple domains of sensory behaviors to accurately identify the needs of toddlers with ASD.