Ablona A, Falasinnu T, Irvine M, et al. - In their prior work, researchers developed a clinical prediction rule (CPR) for predicting asymptomatic chlamydia and/or gonorrhea (CT/NG) infection among women and heterosexual men at in-person STI clinics based on 5 predictors. In the current work, the validity, sensitivity, and overall performance of this CPR was investigated within an Internet-based testing environment (GetCheckedOnline.com). Analysis was performed on GetCheckedOnline online risk assessment and laboratory data from October 2015 to June 2019. The STI clinic population used for CPR derivation (data previously published) was compared with the GetCheckedOnline validation population using χ² tests. Higher asymptomatic CT/NG infection prevalence was recorded in the GetCheckedOnline population (n = 5,478) relative to the STI clinic population (n = 10,437). The CPR showed reasonable calibration and discrimination when it was applied to GetCheckedOnline. Findings support the validity of the application of this existing CPR to detect asymptomatic CT/NG infection within an Internet-based STI testing environment. Online application of clinical prediction rules applied can decrease unnecessary STI testing and optimize resource allocation within publicly funded health systems.