Multifocal brown tumors are a rare complication of primary hyperparathyroidism (PHPT). The reported prevalence of PHPT-related brown tumor is 3-4%. The tumor may histologically resemble any giant cell tumor of the jaws; hence, diagnostic errors or a delayed diagnosis of PHPT, when the lesion is the first clinical manifestation of this disease.We present a 27-year-old patient at 17-week gestation, who was diagnosed with an expansile mass in the left maxilla. Diagnostic tests also revealed two osteolytic lesions in the mandible.The patient underwent left maxillary segmental resection; the tumor was resected en bloc with teeth 25, 26. Histology confirmed the primary diagnosis of giant cell tumor. The observation was continued on an outpatient basis. Following delivery, progression of mandibular osteolytic lesions and maxillary tumor recurrence were found. Blood chemistry panel was ordered and the results raised a suspicion of primary hyperparathyroidism. Subsequent diagnostic tests revealed lower right parathyroid adenoma. Parathyroidectomy resulted in an almost complete regression of the mandibular lesions and a slight regression of the maxillary tumor.The paper presents diagnostic challenges associated with brown tumors as well as clinical, radiological, biochemical and histological manifestations thereof. The effect of pregnancy on the course of primary hyperparathyroidism is discussed and a diagnostic/therapeutic scheme is proposed when giant cells are present in a biopsy specimen.Key words: primary hyperparathyroidism, brown tumor of the maxilla/mandible, giant cell tumor of the maxilla/mandible, pregnancy epulides Słowa kluczowe: pierwotna nadczynność przytarczyc, guz brunatny szczęki i żuchwy, guz olbrzymiokomórkowy szczęki i żuchwy, guzy ciążowe