Temporal artery biopsy (TAB) is one of the diagnostic criteria of giant cell arteritis (GCA) according to 1990 ACR criteria and remains a tool for diagnosis. Although clinicians perform TAB with an intent to confirm suspected GCA, some biopsies result in negative and some lead to non-GCA diagnoses. We aim to review the diagnoses after TAB biopsy performed for suspected GCA and also wanted to evaluate the diagnostic changes and concomitant diseases that develop over time. The patients who had undergone TAB for suspected GCA were identified using the record entry code for TAB. Patients meeting the classification criteria for GCA were designated as the GCA group and not meeting criteria were designated as a non-GCA group. Other classification criteria were implemented for the non-GCA group diseases. A total of 51 patients (Female: 62.7%, median age: 72.1 +/- 7.4 years) who had undergone TAB for suspected GCA were evaluated. TAB was positive in 23 (69.6%) of the 33 patients who met the GCA classification criteria. No significant difference was found between TAB-positive and TAB-negative GCA patients in terms of clinical and laboratory parameters. In the non-GCA group, 12 patients had isolated polymyalgia rheumatica (PMR), and the diagnoses of the remaining six patients were as follows: four large vessel vasculitis (LVV) not satisfying GCA diagnostic criteria, one chronic myelomonocytic leukemia (CMML), and one amyloidosis. TAB was negative in all patients with isolated PMR. TAB showed primary amyloidosis in one patient. Out of 33 GCA patients, 21 had "isolated" GCA, four had GCA + Rheumatoid arthritis (RA), seven had GCA + PMR, and one had GCA + polymyositis. RA was diagnosed antecedent to GCA in two patients, and after GCA in the other two patients. One of the patients had developed GCA 20 years after polymyositis had been diagnosed. TAB was found to be positive in two-thirds of patients with suspected GCA. Late-onset RA and rarely other inflammatory rheumatic diseases may develop in the course of GCA.