Our rationale was to evaluate the accuracy of 1-stop (single patient-attendance) SPECT/CT-guided ultrasound in the localization of parathyroid adenomata. Secondary aims included analyzing the effect of multiple parathyroid adenomata and concurrent thyroid disease on sensitivity. Methods: Patients with hyperparathyroidism who had undergone parathyroidectomy were identified over a 5-y period. Pathologic correlation with results from preoperative 99mTc-sestamibi SPECT/CT followed by targeted ultrasound of the neck was performed. The number of glands, the location, and the presence of concurrent thyroid disease were reviewed. Results: The study included 146 patients (88% single gland, 7% multigland, and 5% negative explorations). The sensitivity and specificity of SPECT/CT-guided ultrasound were 83% and 96%, respectively. The sensitivity was higher for single gland (87%) than multigland disease (70%). The addition of ultrasound significantly increased the sensitivity of the technique (P < 0.001). The presence of concurrent thyroid disease (nodules/thyroiditis) did not adversely affect sensitivity (85% confidence interval, 74.2%-93.1%) compared with normal or atrophic glands (82% confidence interval, 72.3%-89.7%). Conclusion: SPECT/CT-guided ultrasound represents a useful means of localizing parathyroid adenomata, thereby aiding the decision to undertake minimally invasive or exploratory surgery. The 1-stop approach offers patient convenience and enables the radiologist to use the additive benefits of both modalities to optimize localization. The technique is less sensitive in multigland disease, but concurrent thyroid disease does not adversely affect sensitivity.