Proximal surfaces are the second in turn after the occlusal surfaces, as being the most exposed places to the carious process. The specificity of changes and location makes the diagnostic of approximal cavities difficult. The aim of the study was to collect information on possibilities of detection, monitoring and assessment of carious lesions located on proximal surfaces, starting from the early stage. On the base of current literature, chosen methods of diagnosis, from conventional, to advanced technologies were presented. Current literature also suggests that none of the diagnostic methods exclude the possibility of misdiagnosis of proximal caries. Therefore, during the diagnosing of doubtful cases, it is advisable to employ several methods of assessment, with simultaneous individual appraisal of caries risk factors, such as oral hygiene, frequency of eating sweets or the number of active caries foci.