Comparison of body mass index (BMI) was undertaken between 30 cases of salt water drowning and 30 age- and sex-matched controls randomly selected from the autopsy files of Forensic Science SA, Adelaide, Australia, during the period 2000 to 2017. The age range of drowning cases and controls was 18 to 80 (average, 49) years, with a male to female ratio of 19:11. The BMIs of the drowning cases ranged from 15.5 to 37.5 (average, 25.4; median, 23). The control cases had higher BMIs ranging from 22.9 to 44.3 (average, 29.2; median, 25). The number of obese (BMI, ≥30) decedents in the drowning group was 5 (17%) and in the controls was 9 (30%). Individuals who drown in the sea may regularly swim, and thus be fitter and therefore slimmer than more sedentary controls. However, it is also possible that greater amounts of adipose tissue may be protective against drowning, as increased fat stores could improve buoyancy. Thinner individuals with denser body mass may have to struggle more to avoid submersion. It could be that a low BMI is an underappreciated finding that may increase the risk of lethal immersion along with alcohol intoxication and poor swimming skills.