INTRODUCTIONPrimary hyperparathyroidism (PHPT) remains underdiagnosed among patients with hypercalcemia, potentially causing increased morbidity. OBJECTIVETo identify in surgically operated patients the presence of overlooked hypercalcemia and patients with criteria for surgery (CFS) for PHPT at least one year prior to referral to Endocrinology, and to determine whether this diagnostic delay leads to increased morbidity. METHODSAn observational study was carried out in 116 consecutive patients. We evaluated electronic medical records registered at least 12 months prior to referral and divided them in four groups: hypercalcemia with CFS (group 1), hypercalcemia without CFS (group 2), normocalcemia (group 3), and cases without previous biochemical evaluation (group 4). RESULTSA total of 84 patients (72.4%) had a previous measurement of serum calcium at a time interval of ≥ 12 months. Sixty-six (56.9%) had hypercalcemia and 43 of them (37%) had ≥ 1 CFS, with an average delay of 57 months in receiving proper evaluation. Almost half of the calcemia measurements in group 1 had been made in the emergency room. Patients from group 1 were younger, and had a greater frequency of nephrolithiasis and renal impairment than patients in group 4. The serum calcium values at referral were similar in both groups and higher than the values found in patients from the other two groups. DISCUSSIONIn patients with PHPT and CFS, referral to an endocrinologist is made with an average delay of almost 5 years. The identified causes of this delay, which conditions more kidney disease, are unrecognized hypercalcemia and/or unawareness of the surgical criteria, while calcium elevations promote referral. Interventions are needed to avoid this delay in the diagnosis and resolution of PHPT.