Primary hyperparathyroidism (PHP) is an infrequently diagnosed disorder in cats. In this report the signs and symptoms of two cats with hypercalcaemia due to PHP are described, together with diagnostic approach, results of treatment, and immunohistochemical findings. A 9-year-old and a 13-year-old neutered male domestic shorthair cat were presented with signs of lethargy, anorexia, and vomiting. Both cats had persistent hypercalcaemia and normo- to hypophosphataemia. Cytological examination of a fine-needle aspiration biopsy sample of a palpable cervical mass revealed groups of benign glandular-epithelial cells in one cat. In the other cat no cervical mass was palpable. In this cat plasma parathyroid hormone (PTH) levels were measured repeatedly and these values exceeded the maximum reference value on two occasions. Following exclusion of other causes of hypercalcaemia both cats were subjected to neck surgery and in both a solitary parathyroid adenoma was removed. The adenomas contained an abundance of PTH, as demonstrated by immunohistochemical techniques. Plasma calcium and phosphate concentrations returned to within, reference ranges postoperatively. Recovery was uncomplicated and there were no signs of recurrence on follow-up examinations.