Identifying and quantifying the relative frequency of involuntary losses is an essential first step to allow fit-for-purpose herd health programs to be designed for a given cattle production area. The objective of this study was to provide an estimate of the relative frequency of mortality reasons among South Western Australian beef and dairy cattle based on necropsies carried out at a university-based veterinary pathology service for the 38 years from 1 January 1981 to 31 December 2018. A total of 904 cattle were submitted for post mortem examination throughout the study period. Gastrointestinal, cardiopulmonary and reproductive conditions were the most common causes of mortality in beef and dairy cattle submitted for necropsy at Murdoch University for the period 1981 to 2018. In dairy cattle, the common problems were gastrointestinal (18%, 59 of 320), cardiovascular (9%, 30 of 320), and respiratory conditions (8%, 27 of 320). In beef cattle, the most common conditions were gastrointestinal (11%, 39 of 358), reproductive (11%, 38 of 358), cardiovascular (7%, 25 of 358), respiratory (7%, 24 of 358), lameness (6%, 21 of 358), and hepatobiliary conditions (6%, 21 of 358). There is a need to standardise data capture methods, disease definition criteria and more in-depth characterisation of data both at the farm-level and necropsy diagnostic centres.