Autism spectrum disorder symptom emergence is heterogeneous, yet literature comparing young children diagnosed early versus later is relatively scant. Toddlers diagnosed with autism spectrum disorder between 12 and 18 months (n = 20), 19 and 24 months (n = 65), or 25 and 41 months (n = 27) were compared on demographics, developmental functioning, and symptoms. Later diagnosed children were more impaired than both younger groups on nonverbal reasoning, adaptive behavior, and autism spectrum disorder severity. Fine motor, receptive language, and social skills followed a linear pattern, with 25- to 41-month children more delayed than 19- to 24-month participants, who were more delayed than 12- to 18-month toddlers. Communication skills were similarly impaired across groups. Universal autism spectrum disorder screening before 18 months may detect toddlers when symptoms are milder and more amenable to intervention.