OBJECTIVE: To assess the performance of the Cambridge Risk Score (CRS) to predict undiagnosed hyperglycemia in Caribbean and South Asian people living in the U.K. RESEARCH DESIGN AND METHODS: The CRS uses routinely available data from primary care records to identify people at high risk for undiagnosed type 2 diabetes. The sensitivity, specificity, and area under the receiver operator characteristic (ROC) curve for the CRS cut point of 0.199 were 77, 72, and 80% (95% CI 68-91), respectively. The risk score was calculated for 248 Caribbean and 555 South Asian participants aged 40-75 years in the 1999 Health Survey for England. Undiagnosed hyperglycemia was considered present if fasting plasma glucose was >/=7.0 mmol/l or HbA(1c) was >/=6.5%. Sensitivity, specificity, and predictive values were calculated for various cut points of the risk score, and ROC curves were constructed. RESULTS: The area under the ROC curve was 67% (59-76) and 72% (67-78) for Caribbeans and South Asians, respectively. The optimal cut point in Caribbean participants was 0.236, sensitivity was 63% (46-77), and specificity was 63% (56-69). In the South Asian population, the optimal cut point was and 0.127, sensitivity was 69% (60-78), and specificity was 64% (60-69). CONCLUSIONS: The CRS, using routinely available data, can be used in a strategy to detect undiagnosed hyperglycemia in Caribbean and South Asian populations. The existence of ethnic group-specific cut points must be further established in future studies.