The relationship between various technical viewing conditions and the diagnostic value of bitewing radiographs on the interpretation of initial proximal carious lesions was evaluated. Modification of illumination from the viewbox, the masking of the viewbox, the surrounding illumination, viewing against a wide light source, and the use of accessories were studied. Modification of illumination conditions was found to have only a slight negative influence on the diagnostic quality compared to standard conditions. The use of accessories can have a more important, positive influence, especially when one is using a magnifying glass or an x-viewer. TV systems produced disappointing results. The observer, however, proved to be the most important variable with respect to the diagnostic quality of the radiograph.