"Occult" or "hidden" caries refers to occlusal caries which is not diagnosed clinically because the occlusal surface appears ostensibly intact, and radiographs show radiolucencies in dentin. The prevalence of occult caries has been reported to range from 2.2% to over 50% of permanent molars. In spite of its relatively high prevalence, the etiology and pathogenesis of occult caries remain unclear. The author hypothesizes that occult lesions could have resulted from processes which are pre-eruptive or post-eruptive. Pre-eruptive processes include intracoronal resorption of unerupted teeth, and the post-eruptive process is occlusal fissure caries. Although the prevalence of intracoronal resorption has been shown to be around 3-6% by subject and 0.5-2% by teeth, the percentage contribution of this process to the overall prevalence of occult caries is unclear. When affected teeth are fully erupted, it is difficult to determine if pre-eruptive resorption had been present previously. The prevalence of occult lesions does not appear to be affected by fluoride exposure. Radiographs are useful adjuncts to aid in the diagnosis of occult lesions. Bitewing radiographs are useful for detecting early occlusal fissure caries while panorex radiographs of unerupted developing teeth aid in the diagnosis of pre-eruptive intracoronal lesions. It is suggested that all unerupted, developing teeth on radiographs be examined for pre-eruptive resorptive lesions.