PURPOSE Parathyroid adenoma is the most common surgical cause of primary hyperparathyroidism (pHPT). Traditional preoperative localisation of adenomas with Ultrasound (US) or Sestamibi (Mibi) imaging are inconclusive in up to 40%. We aimed to investigate the accuracy of preoperative localisation and postoperative outcomes of four-dimensional computer tomography (4DCT) in patients with discordant US and Mibi. METHOD Patients with discordant US and Mibi, who had undergone surgery for pHPT, were retrospectively recruited from the Monash University Endocrine Surgery Database into ‘4DCT’ or ‘non-4DCT’ groups. Biochemical and surgical data was extracted from electronic medical records, with additional data manually collected from imaging reports. We compared disease aetiology, biochemistry, preoperative localisation accuracy, surgical duration, histopathology, and postoperative outcomes. RESULTS From 2012 to 2023, 370 patients with pHPT and discordant initial imaging underwent parathyroidectomy. Despite similar baseline biochemistry, the ‘4DCT’ group (n=99) included more re-operative patients (8.1% vs 2.2%, p=0.021) compared to the ‘non-4DCT’ group (n=271). Although ‘4DCT’ patients had longer operation time (106min vs 85min, p=0.017), they were more likely to have smaller parathyroid adenomas (0.39g vs 0.5g, p=0.04). Postoperatively, the rate of disease persistence or recurrence was higher in the ‘non-4DCT’ group (11.6% vs 4.1%, p=0.032). CONCLUSION 4DCT can benefit patients requiring further surgery for persistent or recurrent disease and is associated with improved postoperative outcomes, especially when parathyroid adenomas are small. 4DCT should be considered in re-operative cases, or when patients present with discordant US and Mibi findings.