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OBJECTIVES To determine the effectiveness of 99m Tc-sestamibi renal SPECT/CT in distinguishing between malignant and benign renal lesions. PATIENTS AND METHODS Between June 2018 and October 2020 all patients with new indeterminate small renal masses (SRMs) underwent 99m Tc-sestamibi renal SPECT/CT prior to biopsy or surgery. The accuracy of 99m Tc-sestamibi imaging diagnoses was assessed against histopathology. Receiver operating characteristic (ROC) analysis was used to determine the optimum cut-off for the tumour:normal uptake ratio. Logistic regression was used to determine if quantitative analysis significantly added to visual interpretation alone. RESULTS A total of 74 patients with SRMs were investigated with 99m Tc-sestamibi SPECT/CT. SPECT/CT correctly identified 49 malignant tumours and 11 benign tumours, resulting in a sensitivity of 0.89 [95% CI: 0.77 - 0.95] and a specificity of 0.73 [95% CI: 0.45 - 0.91]. ROC analysis of uptake ratios demonstrated that a tumour:normal uptake ratio of 0.41 provided optimal diagnostic accuracy (sensitivity 0.81, specificity 0.88, area under the curve 0.883 [95% CI:0.794 - 0.971]). The uptake ratio was also highly significant in excluding malignancy on univariate logistic regression analysis whereby the higher the uptake ratio, the lower the chances were for malignancy (OR 0.009,95% CI: 0.001-0.118, p < 0.001. However, this did not improve diagnostic accuracy when compared to visual interpretation alone. CONCLUSION 99m Tc-sestamibi SPECT/CT is a non-invasive technique with good accuracy in determining if a SRM is benign or malignant.