Primary hyperparathyroidism secondary to true sporadic synchronous parathyroid cancer (PTCa) and adenoma (PTa) is rare. This is a case of an 80-year-old female admitted with symptomatic hypercalcaemia, raised serum calcium (Ca) of 3.39 mmol/L and raised parathyroid hormone (PTH) of 44.3 pmol/L. Ultrasonic evaluation of the neck revealed a mass posterior to the right thyroid lobe. Imaging of the left neck was unremarkable. Subsequent sesta-MIBI and single-photon emission computed tomography-computed tomography (SPECT-CT) scanning highlighted conspicuous activity over the right lower neck consistent with the neck ultrasound scan findings. Pre-operatively, PTa was suspected. Intra-operatively, malignancy was suspected due to infiltration of the parathyroid tumour into the thyroid. The right inferior parathyroid and right thyroid gland were resected. Histology confirmed PTCa. Despite surgical treatment, she was found to have persistently high Ca and PTH levels. Further investigation with a repeat sesta-MIBI and SPECT-CT suggested a left inferior parathyroid tumour. Excision of this mass revealed a PTa. Recovery was unremarkable and serum biochemistry returned to normal ranges.