Background: Prolonged Grief Disorder (PGD) is a new disorder. A structured clinical interview for ICD-11 and DSM-5-TR PGD is a necessary tool in diagnosing PGD needed as PGD is implemented as a mental disorder in health services across the world.Objective: This study developed and validated The Aarhus PGD Interview (A-PGDi) to provide clinicians with free access to a valid method to diagnose PGD in alignment with recent diagnostic requirements in ICD-11 and DSM-5-TR and to training materials.Method: The A-PGDi was developed in close collaboration between scientists, clinicians, and bereaved individuals. First, all PGD-symptoms underwent two rounds of item-formulations by clinicians and researchers. Then, a first version of the A-PGDi was tested in a group of bereaved adults with PGD symptoms, who were interviewed about the A-PGDi. The A-PGDi was refined according to their responses, piloted in 13 bereaved adults and further refined to its final version. The validity of A-PGDi was then tested with clinical interviews for PGD, PTSD, depression, and anxiety performed by carefully trained clinical interviewers in a sample of 124 bereaved adults (mean age 47 years (range 19-83 years); 85% female).Results: Benchmarked against a self-report measure of PGD and moderate to substantial inter-diagnostic agreement between ICD-11 and DSM-5-TR diagnoses the A-PGDi had sufficient content validity. Significant relations between PGD-diagnosis and other mental disorders estimated with clinical interviews and self-report scales and moderate to substantial inter-diagnostic and test-retest agreement indicated sufficient criterion validity and reliability.Limitations: small non-probability sample with PGD symptoms; self-identified for participation; mostly female.Conclusions: The results indicate that A-PGDi with some limitations is a valid structured clinical interview for diagnosing both ICD-11 and DSM-5-TR PGD that is relevant to administer in mental health settings to ensure correct diagnostics and the most helpful treatment plan for people with PGD.