AbstractEmotion dysregulation (ED) is common and severe in older autistic youth, but is rarely the focus of early autism screening or intervention. Moreover, research characterizing ED in the preschool years (when autism is typically diagnosed) is limited. This study aimed to characterize ED in autistic children by examining (1) prevalence and severity of ED as compared to children without an autism diagnosis; and (2) correlates of ED in autistic children. A sample of 1864 parents (Mean child age = 4.21 years, SD = 1.16 years; 37% female) of 2–5 year‐old children with (1) autism; (2) developmental concerns, but no autism; and (3) no developmental concerns or autism completed measures via an online questionnaire. ED was measured using the Emotion Dysregulation Inventory‐Young Child, a parent report measure characterizing ED across two dimensions: Reactivity (fast, intense emotional reactions) and dysphoria (low positive affect, sadness, unease). Autistic preschoolers, compared to peers without developmental concerns, had more severe ED (+1.12 SD for reactivity; +0.60 SD for dysphoria) and were nearly four and three times more likely to have clinically significant reactivity and dysphoria, respectively. Autistic traits, sleep problems, speaking ability, and parent depression were the strongest correlates of ED in the autism sample. While more work is needed to establish the prevalence, severity, and correlates of ED in young autistic children, this study represents an important first step. Results highlight a critical need for more high‐quality research in this area as well as the potential value of screening and intervention for ED in young autistic children.