A 57-year-old woman with type 2 diabetes was admitted to our hospital presenting with generalized bone pains, hypercalcemia, and elevated parathyroid hormone level. Enhanced CT scan demonstrated a large soft tissue mass in the right anterior mediastinum. Tc-MIBI scintigraphy revealed the focal accumulation of radiotracer uptake in the anterior mediastinum. Tc-MIBI SPECT/CT imaging also corroborated the same finding. The patient underwent surgery to have a giant ectopic parathyroid adenoma (7 × 4.5 × 1.5 cm) removed. The patient has been observed for 2 years, with normal parathyroid hormone and calcium levels.