Episodes of crying with higher fundamental frequency (f0) are perceived as more aversive and distressful than lower frequency cries. Besides, previous studies have speculated that in children with Autism Spectrum Disorder (ASD) higher f0 may account for evoking mental states of uneasiness in the caregiver. Moreover no evidence on developmental trajectory of f0 in ASD in infancy is present in literature. This research investigated: developmental trajectory of f0 of episodes of crying in children with ASD as opposed to typically developing (TD) children and children with other developmental delay (DD). Two studies were employed. In Study 1, using a standardised protocol for acoustic analysis a group of 30 TD children was followed longitudinally (five, 13 and 20 months) and f0 of their episodes of crying was analysed. In Study 2, acoustic analysis was applied to episodes of crying selected from retrospective home videos of 30 children with ASD, TD and DD at five and 18 months. Decrease of f0 in TD children between the first and second year both using a standard procedure and the retrospective procedure was found. Besides while in TD and DD children a change of the f0 trajectory was present, no changes were evident in ASD. Higher f0 may account in ASD for a caregiver bias in their interpretation of crying, evoking mental states of uneasiness and it may interfere with the adequacy of the parental response. Limitations and future goal of the research are described. (Contains 2 figures.)