After resection of oropharyngeal tumors, 175 dental implants were placed in 18 irradiated (average = 44 Gy) and 22 non-irradiated patients between 1988 and 1997. Within a control period of 37 months on average, 15 implants failed. The reasons for implant failures were analysed. The analysis of implant failures revealed indicative parameters. Primary failure of 11 implants (interval between implant placement and abutment placement) was recognized in four irradiated and two non-irradiated oral cancer patients. These fixtures showed no osseointegration during the healing period due to a mandibular fracture, overloading or unknown etiology. After prosthodontic rehabilitation four implants in two irradiated and two non-irradiated oral cancer patients were removed (secondary failure). These secondary losses occurred at an average of 39 months after second stage surgery and were caused by biomechanical overloading or peri-implant infection. No osteoradionecrosis development due to implant failure was observed in irradiated patients. In all cases, peri-implant pocket depth, implant stability and peri-implant bone resorption increased before definitive secondary implant failure. Therefore, these findings seem to be useful as indicative parameters in the prediction of implant failure. Schlagwörter: endosseous implants, oral cancer patients, irradiation, implant failure