Purpose: To evaluate the reliability of a conometric system for fixed retention of complete prostheses (CPs) on four implants after 5 years of function. Materials and methods: Twenty-five patients with a completely edentulous mandible received four implants supporting a CP. A total of 100 implants were immediately loaded with CPs on conometric abutments. A follow-up of 5 years was observed for each patient. Outcome measures were prosthesis and implant success, complications, probing pocket depth changes, marginal bleeding and plaque changes, and patient satisfaction. Results: One patient dropped-out. In total, 96 implants supporting the 24 CPs completed the follow-up examination at 5 years. No implant failed. Two framework fractures occurred after 4 and 5 years of function. No loss of retention was recorded for the CPs. Mucositis was recorded for two implants after 1 year of prostheses function for two patients, for one implant after 3 years and for two implants after 4 years in different patients and successfully treated with interceptive supportive therapy. No significant differences were found between Plaque Index (PI) at baseline and after 2 years (P = 1.0); similar findings were calculated between PI at baseline and after 5 years (P = 0.6) of function. At baseline, after 2 and after 5 years, respectively, 69%, 64% and 56% of implants showed a PI of 0; 31%, 36% and 44% of implants showed a PI between 1 and 3. Modify Bleeding Index (MBI) was not significantly different both between baseline and after 2 years of function (P = 1.0) and between baseline and 5 years of function (P = 0.5). At baseline, after 2 and after 5 years, respectively, 69%, 65% and 61% of implants showed a MBI of 0; 27%, 28% and 29% of implants showed a MBI of 1; and 4%, 7% and 10% of implants showed a MBI of 2. The mean probing pocket depth was 1.2 ± 0.4 mm at baseline, 1.2 ± 0.4 mm after 2 years and 1.4 ± 0.5 mm after 5 years of function. The differences were not statistically significant between baseline and 2 years (P = 1.0) and between baseline and 5 years (P = 0.1). From the patient satisfaction questionnaire, 85% percent of patients were satisfied from both aesthetic and functional points of view after 5 years of conometric prostheses function. Conclusions: The present implant-supported conometric retention system can be used to give fixed retention to a CP supported by four implants. An adequate metal framework should be provided to the definitive restoration in order to avoid fractures in the long term.