Opercula of permanent first and second molars delayed in eruption were investigated histologically to detect possible causes of eruption failure. The material comprised operation specimens from exposure of 74 non‐erupted molars in 63 young individuals (34 boys. 29 girls). Eighteen of the 74 specimens (or 24.3%) were diagnosed as “classical” odontogenic tumors belonging to the following entities: ameloblastic fibroma (seven), ameloblastic flbrodentinoma (six), ameloblastic fibro‐odontoma (four) and complex odontoma (one). Twenty‐two specimens (or 29.7%) showed a hitherto unrecognized odontogenic lesion of hamartomatous character, termedodontogenic giant cell fibromatosis IGCF).Thus, 54.1% of the specimens could be diagnosed as odontogenic tumors or humartomas. Histomorphologic changes could not be detected in the remaining 34 specimens (45.9%). Odontogenic tumors were associated with uneruptedfirstmolars much more frequently than withsecondmolars (ratio 8:1). The OGCF had a strong association with uneruptedmandibularmolars. Further, opercula ofmandibular firstmolars frequently revealed odontogenic lesions whereas tissue overlying the crown of uneruptedmaxillary secondmolars often was reported as normal