The Structured Interview for Hoarding Disorder (SIHD) is a semi-structured instrument designed to assist clinicians and trained interviewers with the nuanced diagnosis of hoarding disorder (HD). The manuscript introduces the rationale, development, and design of the SIHD and presents a test of the instrument's inter-rater reliability and convergent/discriminant validity. Ninety-nine individuals with self-reported hoarding behavior, originally recruited as part of a large two-wave epidemiological study, were evaluated in their homes using the SIHD. Diagnoses of HD were determined by consensus, following a best estimate diagnosis procedure. To enable the assessment of inter-rater reliability, a psychiatrist with extensive experience diagnosing HD also independently and blindly reviewed each participant's SIHD. In addition, agreement of SIHD diagnoses with those indicated by other screening instruments for HD and depression were examined. Results indicate “substantial” or “near perfect” inter-rater reliability for all core HD criteria and specifiers. Convergent and discriminant validity were, furthermore, excellent. Overall, the SIHD offers an intuitive, valid, and reliable means of diagnosing HD. The interview also facilitates the assessment of other relevant features, such as risk. We offer recommendations for its use in both research and clinical settings, as well as suggestions for the training of interviewers.