Diagnosing frailty syndrome at autopsy may be difficult if no adequate clinical history is provided. As low body mass index (BMI) may be associated with frailty in the elderly, the following study was undertaken to determine the percentage of medicolegal cases with BMIs < 18.5 in decedents aged over 75 years. Review was undertaken over three time periods: January to December 1986, January to December 2006, and January to December 2012. In 1986, 16% (15 of 93) of individuals aged ≥75 years had BMIs < 18.5, in 2006, 15% (50 of 336), and in 2012, 13% (35 of 274). In no case was frailty syndrome mentioned. This study demonstrates that frailty syndrome appears to be an underappreciated diagnosis in forensic practice despite a significant percentage of elderly decedents (13–16% over a 27-year period) having low BMIs. Prospective assessment of this group is required to determine the incidence and contribution to mortality of frailty syndrome in a forensic context.