PURPOSE: To conduct an initial psychometric evaluation of the reliability and validity of the Hypoparathyroidism Symptom Diary (HPT-SD). PATIENTS AND METHODS: Data were collected during a cross-sectional, observational study. Participants with self-reported hypoparathyroidism (HPT) completed the HPT-SD, the Functional Assessment in Cancer Therapy-Cognitive Function (FACT-Cog), the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue), and the Hospital Anxiety and Depression Scale (HADS) measures. Item- and scale-level internal consistency reliability, known-groups validity, and construct validity were evaluated. Subscales were identified and preliminary scoring algorithms were developed. RESULTS: The study included 52 participants (mean age, 51 years). Overall, the measurement properties of the HPT-SD were very good. Item-level response frequency distributions showed evidence of possible floor effects for four muscle-related symptom items. Inter-item correlations revealed a pattern of relationships among symptom items (r=0.3-0.8) and among impact items (r=0.5-0.7) and provided evidence for two HPT-SD subscales: Symptoms and Impacts. Construct validity correlations supported a priori convergent validity hypotheses (|r|≥0.4) between HPT-SD subscales and the FACT-Cog, FACIT-Fatigue, and HADS. Mean HPT-SD Symptom and Impact scores were in the expected direction and significantly different between subgroups of patients with high and low HPT disease severity. CONCLUSION: Results indicate that the HPT-SD is an appropriate measure of HPT-related symptoms and impacts. Floor effects may be attributed to the observational study design: participants manage symptoms with calcium and active vitamin D supplements prior to an escalation in severity. Future studies should assess the HPT-SD measurement properties using longitudinal study designs.