The objective of the present study was to elicit opinion from two groups of veterinarians [subject matter experts and non-subject matter experts] about the causes of bovine perinatal mortality and the criteria used to assign such causes. The subject matter experts were selected on the basis of their scientific publications or experience of working in a veterinary diagnostic or research laboratory in the area of bovine perinatal mortality. The non-subject matter experts were self-selected as cattle veterinarians without particular expertise in bovine perinatology. A total of 74 veterinarians (46 subject matter experts and 28 non-subject matter experts) from 23 countries responded. The study was conducted using Delphi methodology over seven rounds. Respondents were asked to agree the causes of bovine perinatal mortality and for each cause to agree the supporting diagnostic criteria. There was a close agreement between groups on 16 causes of death apart from intra-uterine growth retardation (IUGR) and micronutrient imbalances which were accepted by fewer subject matter experts. There was inter-group consensus on the criteria to diagnose accidents, congenital defects, dystocia, hyperthermia, infections, premature placental separation, prematurity and prolonged calving. There was inter-group consensus on the criteria to diagnose anoxia, apart from gingival cyanosis; on haemorrhage, apart from haemorrhagic anaemia; on IUGR, apart from organ weights; and on iodine imbalance, apart from goitre and thyroid iodine content. The results from this study highlighted the current lack of standardization of the criteria used to define the cause of death for bovine perinatal mortality and the need for such standardization.