Objective: To describe the diagnostic performance of SolarScan (Polartechnics Ltd, Sydney, Australia), an automated instrument for the diagnosis of primary melanoma. Design: Images from a data set of 2430 lesions (382 were melanomas; median Breslow thickness, 0.36 mm) were divided into a training set and an independent test set at a ratio of approximately 2: 1. Adiagnostic algorithm (absolute diagnosis of melanoma vs benign lesion and estimated probability of melanoma) was developed and its performance described on the test set. High- quality clinical and dermoscopy images with a detailed patient history for 78 lesions (13 of which were melanomas) from the test set were given to various clinicians to compare their diagnostic accuracy with that of SolarScan. Setting: Seven specialist referral centers and 2 general practice skin cancer clinics from 3 continents. Comparison between clinician diagnosis and SolarScan diagnosis was by 3 dermoscopy experts, 4 dermatologists, 3 trainee dermatologists, and 3 general practitioners. Patients: Images of the melanocytic lesions were obtained from patients who required either excision or digital monitoring to exclude malignancy. Main Outcome Measures: Sensitivity, specificity, the area under the receiver operator characteristic curve, median probability for the diagnosis of melanoma, a direct comparison of SolarScan with diagnoses performed by humans, and inter instrument and intra instrument reproducibility. Results: The melanocytic- only diagnostic model was highly reproducible in the test set and gave a sensitivity of 91% (95% confidence interval [CI], 86% - 96% ) and specificity of 68% (95% CI, 64% 72% ) for melanoma. SolarScan had comparable or superior sensitivity and specificity (85% vs 65% ) compared with those of experts (90% vs59% ), dermatologists (81% vs 60% ), trainees (85% vs 36% ; P=. 06), and general practitioners (62% vs 63% ). The intraclass correlation coefficient of intra instrument repeatability was 0.86 (95% CI, 0.83- 0.88), indicating an excellent repeatability. There was no significant inter instrument variation (P=.80). Conclusions: SolarScan is a robust diagnostic instrument for pigmented or partially pigmented melanocytic lesions of the skin. Preliminary data suggest that its performance is comparable or superior to that of a range of clinician groups. However, these findings should be confirmed in a formal clinical trial. Design: Images from a data set of 2430 lesions (382 were melanomas; median Breslow thickness, 0.36 mm) were divided into a training set and an independent test set at a ratio of approximately 2: 1. Adiagnostic algorithm (absolute diagnosis of melanoma vs benign lesion and estimated probability of melanoma) was developed and its performance described on the test set. clinical and dermoscopy images with a detailed patient history of 78 lesions (13 of which were melanomas) from the test set were given to various clinicians to compare their diagnostic accuracy with that of SolarScan. Settings: Seven specialist referral centers and 2 general practice skin cancer clinics from 3 continents. Comparison between clinician diagnosis and SolarScan diagnosis was by 3 dermoscopy experts, 4 dermatologists, 3 trainee dermato logists, and 3 general practitioners. Patients: Images of the melanocytic lesions were obtained from patients who required either excision or digital monitoring to exclude malignancy. Main Outcome Measures: Sensitivity, specificity, the area under the receiver operator characteristic curve, median probability for the diagnosis of melanoma, a direct comparison of SolarScan with diagnoses performed by humans, and inter instrument and intra instrument reproducibility. Results: The melanocytic-only diagnostic model was highly reproducible in the test set and gave a sensitivity of 91% (95% confidence interval (95% CI, 64% 72%) for melanoma. SolarScan had comparable or superior sensitivity and specificity (85% vs 65%) compared with those of experts % vs59%), dermatologists (81% vs60%), trainees (85% vs36%; P = .06), and general practitioners (62% vs63%). The intraclass correlation coefficient of intra-instrument repeatability was 0.86 95%CI was 0.83-0.88), indicating an excellent repeatability. There was no significant inter instrument variation (P = .80). Conclusions: SolarScan is a robust diagnostic instrument for pigmented or partially pigmented melanocytic lesions of the skin. Preliminary data suggest that its performance is comparable or superior to that of a range of clinician groups. However, these findings should be confirmed in a formal clinical trial.