Distinguishing a disorder of persistent and impairing grief from normative grief allows clinicians to identify this often undetected and disabling condition. As four diagnostic criteria sets for a grief disorder have been proposed, their similarities and differences need to be elucidated.

Participants were family members bereaved by US military service death (N = 1732). We conducted analyses to assess the accuracy of each criteria set in identifying threshold cases (participants who endorsed baseline Inventory of Complicated Grief ⩾30 and Work and Social Adjustment Scale ⩾20) and excluding those below this threshold. We also calculated agreement among criteria sets by varying numbers of required associated symptoms.

All four criteria sets accurately excluded participants below our identified clinical threshold (i.e. correctly excluding 86–96% of those subthreshold), but they varied in identification of threshold cases (i.e. correctly identifying 47–82%). When the number of associated symptoms was held constant, criteria sets performed similarly. Accurate case identification was optimized when one or two associated symptoms were required. When employing optimized symptom numbers, pairwise agreements among criteria became correspondingly ‘very good’ (κ = 0.86–0.96).

The four proposed criteria sets describe a similar condition of persistent and impairing grief, but differ primarily in criteria restrictiveness. Diagnostic guidance for prolonged grief disorder in International Classification of Diseases, 11th Edition (ICD-11) functions well, whereas the criteria put forth in Section III of Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) are unnecessarily restrictive.

The World Health Organization (WHO) International Classification of Disease (ICD-11) is expected to include a new diagnosis for prolonged grief disorder (ICD-11PGD). This study examines the validity and clinical utility of the ICD-11PGD guideline by testing its performance in a well-characterized clinical sample and contrasting it with a very different criteria set with the same name (PGDPLOS).

We examined data from 261 treatment-seeking participants in the National Institute of Mental Health (NIMH)-sponsored multicenter clinical trial to determine the rates of diagnosis using the ICD-11PGD guideline and compared these with diagnosis using PGDPLOS criteria.

The ICD-11PGD guideline identified 95.8% [95% confidence interval (CI) 93.3–98.2%] of a treatment-responsive cohort of patients with distressing and impairing grief. PGDPLOS criteria identified only 59.0% (95% CI 53.0–65.0%) and were more likely to omit those who lost someone other than a spouse, were currently married, bereaved by violent means, or not diagnosed with co-occurring depression. Those not diagnosed by PGDPLOS criteria showed the same rate of treatment response as those who were diagnosed.

The ICD-11PGD diagnostic guideline showed good performance characteristics in this sample, while PGDPLOS criteria did not. Limitations of the research sample used to derive PGDPLOS criteria may partly explain their poor performance in a more diverse clinical sample. Clinicians and researchers need to be aware of the important difference between these two identically named diagnostic methods.