In a continuous process such as caries, it is important to possess criteria or instruments that allow the lesions to be diagnosed at early stages so that preventive or interceptive treatments can be applied before cavitation takes place. The present study seeks to assess the diagnostic efficacy of the International Caries Detection and Assessment System (ICDAS II) criteria and the DIAGNOdent laser fluorescence (LF) pen in occlusal caries lesions, using histological sections as the gold standard. Sixty-four permanent teeth were examined by two researchers who previously performed and calibrated both the ICDAS II criteria and the use of DIAGNOdent pen. The teeth were then cut into sections and observed under an optical microscope. The sensitivity values were 0.82 (ICDAS II) and 0.85 (LF). The specificity values were 1.00 (ICDAS II) and 0.53 (LF). The intraexaminer reproducibility was 0.892 for ICDAS II and 0.912 for the DIAGNOdent, so it was high for both diagnostic methods. However, the DIAGNOdent pen showed greater sensitivity and the ICDAS criteria more specificity. It was concluded that both methods are efficacious individually but combining the two is recommended to improve the diagnosis.