Objectives This study explored unintentional fatal drowning among children and adolescents (0–19 years) diagnosed with autism spectrum disorder (ASD) in Australia.

Design This total population, cross-sectional audit used data from the Royal Life Saving National Fatal Drowning Database to explore demographic and causal factors in ASD drowning cases between 1 July 2002 and 30 June 2018. Rates and relative risk (RR) with a 95% confidence interval (CI) were calculated for drowning cases with and without ASD, using estimated population-level prevalence data.

Results Of the 667 cases of drowning among 0–19 year olds with known medical history, 27 children and adolescents (4.0%) who drowned had an ASD diagnosis. Children and adolescents with ASD were three times more likely to drown than those without ASD (RR=2.85; CI 0.61 to 13.24). Among those with ASD, 0–4 year olds record the highest rate (11.60/100 000 diagnosed). Children and adolescents with ASD were significantly more likely to drown when compared with those without ASD: if aged 5–9 years (44.4% of ASD-yes cases; 13.3% of ASD-no cases); in a lake or dam (25.9% vs 10.0%) and during winter (37.0% vs 13.1%).

Conclusion Heightened awareness of drowning risk for children and adolescents with ASD is required, including adult supervision and barriers restricting water access. Further evaluation of the effectiveness of personal alarms to alert caregivers to an unsupervised child is warranted. Challenges exist regarding accurate estimates of population-level ASD prevalence and identification of ASD in coronial files. As the diagnosis of ASD does not often occur until age five, results may be an underestimate.