This study was designed to assess the feasibility and practicability of the employment of endoscopic methods for the diagnosis of dental caries and to compare the diagnostic performance, in posterior teeth, of visual endoscopic caries diagnosis (with and without the benefit of differential fluorescence) with that of conventional visual diagnosis, bitewing radiographi, and conventional transillumination. The two endoscopic methods were found to be clinically practicable, to be able to demonstrate the presence of small carious lesions, and to have both advantages and disadvantages compared to conventional methods. When all tooth sites were compared, the results indicated that the endoscopic methods may detect a greater number of carious lesions than do conventional visual, radiographic, or fiber-optic transilluminational methods of caries diagnosis. Further investigations involving histologic validation of diagnoses as well as larger numbers of patients and multiple examiners are indicated.