Primary hyperparathyroidism is now predominantly an asymptomatic pathology, as blood calcium assay has become systematic. Diagnosis therefore requires screening for target organ damage when this is not already indicative of primary hyperparathyroidism. Classical clinical manifestations include bone, kidney and muscle signs, and are characterized by reversibility after parathyroid surgery. Their presence requires blood calcium assay. Non-classical manifestations include cardiovascular, digestive and neuropsychological signs, which are not known to be reversible after surgery. Positive diagnosis is biological, based on a parathyroid hormone value that is inappropriate to the blood calcium value. The typical form combines hypercalcemia, elevated parathyroid hormone and increased calciuria or calcium excretion fraction. Atypical forms combine either hypercalcemia and normal parathyroid hormone level, or normal calcemia with increased parathyroid hormone level, not necessarily secondary to another cause, such as 25(OH) vitamin D deficiency. The oral calcium loading test and the Pro-FHH score are contributive to diagnosis in atypical forms.