Background: Sensory modulation difficulties are common in children with conditions such as Autism Spectrum Disorder (ASD), and could contribute to other social and non-social symptoms. Positing a causal role for sensory processing differences requires observing atypical sensory reactivity prior to the emergence of other symptoms, which can be achieved through prospective studies of elevated likelihood populations. Methods: We examined auditory habituation and change detection in 5 and 10-month-old infants with and without Neurofibromatosis Type 1 (NF1), a condition associated with higher likelihood of developing ASD. Results: in typically developing infants, habituation to vowel repetition and enhanced responses to vowel/pitch change decreased with age over posterior regions; age-related change was diminished in the NF1 group. Whilst both groups detected changes in vowel and pitch, the NF1 group were largely slower to show a differentiated neural response. Auditory responses did not relate to later language but were related to later ASD traits. Conclusions: These findings represent the first demonstration of atypical brain responses to sounds in infants with NF1, and suggests they may relate to the likelihood of later ASD.