This study compared the experiences with surgical procedures and treatment effects of a mainly implant-supported overdenture retained by a transmandibular implant with those of an implant tissue-supported overdenture retained by two cylindrical endosseous implants. Treatment had been assigned according to a balanced allocation method to 95 patients, including a control group who received only conventional complete dentures. Since some of the patients refused the allocated treatment, the "intention to treat" analysis was applied. The results show that the experiences with surgical procedures were significantly more positive for the transmandibular implant group than the endosseous implant group. The differences with respect to satisfaction, complaints, and subjective chewing ability were not statistically significant. These results were unexpected because the overdentures retained by the transmandibular implants were, to a much larger extent, supported by the implant than were the overdentures retained by two endosseous implants. Palabras clave: clinical trial, dental implants, denture satisfaction, overdentures