Our team examined 150 reports on group-design, non-pharmacological interventions for young autistic children, to determine the prevalence of adverse event reporting. We found that only 11 studies mentioned adverse events; one indicated adverse events occurred, and an additional three indicated adverse "effects" occurred (i.e. adverse events that could be attributed to the intervention). We also coded reasons for participant withdrawal and found that of the 54 studies that reported reasons for withdrawal, 10 studies reported reasons that could be categorized as adverse events, 8 reported reasons that could be categorized as adverse effects, and an additional 12 studies reported reasons that were too vaguely described to determine adverse event status. We recommend that autism intervention researchers make concerted efforts to monitor, classify, and report adverse events so that practitioners, policy-makers, and families are better equipped to weigh potential benefits of interventions against potential harms.