AIM: To review the occurrence of prosthetic failure and biological complications with respect to the crown to implant (C/I) ratio. METHODS: Accurate search was made on the subject C/I ratio with the following criteria: (1) studies on humans with data on prosthetic failure and/or biological complications related to C/I ratio; (2) partial edentulous patients; (3) randomized clinical trials, prospective, longitudinal, retrospective, and multicenter studies with a minimum of 48 months mean follow-up; (4) language: English; (5) radiographic measurements by peri-apical X-ray; (6) implant material: titanium; and (7) no implant type selection was applied. RESULTS: Six articles were considered eligible for full-text analysis. Unfavorable C/I ratio can be considered a potential risk factor for single crown and abutment loosening (C/I ratio ≥1.46) and abutment fractures in posterior areas (C/I ratio ≥2.01). CONCLUSIONS: Despite the limited data, high C/I ratio may be related to some prosthetic failures. Unfavorable C/I ratio does not affect biological complications and implant failure.