The aim of this in vivo study was to evaluate the effectiveness of DIAGNOdent, visual and radiographic examination in detecting non-invasive diagnosis of occlusal caries in children. In this study, 92 untreated molars with sound occlusal surface or enamel and/or dentin caries were selected from 28 healthy patients, aged 7-17 years. All teeth were examined by two researchers using each of three diagnostic system (DIAGNOdent, visual, radiographic). Interpretation of the DIAGNOdent value and the radiolucency on the bitewing film were combined with the visual examination to decide where the teeth had to be opened. Depth of caries was recorded. Sensitivities and specificities were calculated for each diagnostic method using the biopsy scores as gold standard. Intra- and inter-examiner reproducibility for each method was assessed by calculating Cohen's kappa. The kappa value of inter-examiner reproducibilty was highest for visual examination (0.935), and lowest for DIAGNOdent measurements (0.698). Intra-examiner reproducibilty of DIAGNOdent mesurements was also good (0.745 and 0.665). Sensitivity and specificity for DIAGNOdent, visual examination and bitewing radiography were 0.86/0.80, 0.69/1.00 and 0.36/1.00, respectively. It was concluded that Diagnodent with a high sensitivity may be useful adjunct to visual examination with a high specificity in detecting occlusal caries.