This study consists of four parts, the eligibility criteria of each part is described below:  Part 1:  Search criteria of chronic HP:  Inclusion Criteria:  Existing diagnosis of HP  Exclusion Criteria:  Age<18 at the time of screening  Search criteria of suspected HP:  Inclusion Criteria:  Hypocalcemia plus neck surgery Hypocalcemia plus convulsions/tetany/epilepsy Hypocalcemia plus PTH<upper limit, and no hypoalbuminemia Hypocalcemia without any of the following conditions: neck surgery, convulsions/tetany/epilepsy, PTH testing, hypoalbuminemia, critical illness and vitamin D deficiency-related diseases.  Exclusion Criteria:  Age<18 at the time of screening  Diagnosis of chronic HP:  Inclusion Criteria:  Hypocalcemia (albumin adjusted total calcium < lower limit) with inappropriate reduction of serum PTH level (PTH < upper limit). The course of hypoparathyroidism should be more than 6 months.  Part 2  Inclusion Criteria:  Patients with chronic HP confirmed through medical records review Patients with suspected HP confirmed through medical records review Obtain written informed consent  Exclusion Criteria:  Non-local residents  Part 3  Inclusion Criteria:  Patients with chronic HP Participating in the on-site survey in the Peking Union Medical College Hospital  Part 4  Inclusion criteria:  Endocrinologists involved in HP care from 7 sites Obtain written informed consent