Tertiary Hyperparathyroidism (HPT) is an uncommon condition that affects patients with secondary HPT after a successful kidney transplant. Bone alterations are the main consequences of this endocrine condition, including the development of an osteolytic lesion called brown tumour. This paper reports an unusual case of multiple brown tumours located in the maxilla and mandible in a 58-year-old renal transplant recipient, with tertiary HPT. Incisional biopsies were performed and, in both samples, the histopathological diagnoses were giant cell lesions. Due to these diagnoses, the medical history of chronic renal failure, and high levels of serum calcium and PTH, lesions were diagnosed as multiple brown tumours of tertiary HPT. The lesions showed regression within the two months following a total parathyroidectomy. Minimal local interventions were established to make an early diagnosis and to treat these lesions. The diagnosis of primary oral lesions was very important in order to demonstrate the relevance of interdisciplinary activity and the inclusion of dentists as part of organ transplant units.