The term 'hidden caries' is used to describe a carious lesion seen in dentine on a bitewing radiograph where clinically the occlusal enamel appears sound or only minimally demineralized. The relative rise in the number of clinically sound occlusal surfaces over the past two decades could be a reason why hidden caries has come into sharper focus for practitioners and researchers. Dentists, routinely examining children who are clinically caries-free, may be shocked to discover a large lesion on a radiograph that they have apparently missed clinically. This underlines the importance of careful examination of the radiograph. It is important that the practitioner appreciates the possibility of hidden caries, and the value of the radiograph in its diagnosis.