The nature of hyperresponsiveness to sensory stimuli in children with autism, using a new observational measure, the SPA, was examined. Three groups of young participants were assessed (autism, developmental delay, typical). Across all groups, MA was a predictor of hyperresponsiveness, such that aversion to multisensory toys decreased as MA increased. The two clinical groups displayed higher levels of sensory aversion than the typical group. The groups did not differ in the proportion of children habituating to an auditory stimulus; however, nonresponders were more prevalent in the autism group. These findings elucidate developmental influences on sensory features and the specificity of hyperresponsiveness to clinical groups. Implications for understanding pathogenesis, differentiating constructs of hypersensitivity, and planning treatment are discussed.