Background and Aim: Metal-ceramic crowns have been considered an acceptable treatment plan for the rehabilitation of edentulous patients in implant dentistry. Furthermore, porcelain fractures associated with an implant-supported metal-ceramic crown occur more than tooth-supported restorations; then, assessment of the associated factors in this regard needs more studies. The present study evaluated porcelain fractures in the implant-supported crowns compared to the tooth-supported metal-ceramic crowns in the patients referred to the Specialist Ward of Fixed Prosthodontics, Shahid Beheshti University of Medical Sciences, Dental School during 2001-2010.Materials and Methods: In this retrospective descriptive study, 42 patients (24 males, 18 females) having received implant or tooth-supported metal-ceramic crowns were underwent follow-up examinations by two operators. There were 185 tooth-supported and 158 implant-supported units in total. Porcelain fractures were assessed regarding California Dental Association criteria (severe, small, no fracture). The presence of parafunctional habits, opposing dentition, treatment location, type of prostheses, implant system, type of occlusion, number of prostheses units and the applied cements were determined in the prostheses. The results were reported by descriptive statistics and the data statistically compared by Chi-square and Exact Fisher tests as well as odd’s ratio calculation.Results: Porcelain fracture occurred in 5.4% tooth-supported (1.6% severe and 3.8% small ratings) and 10.2% implant-supported (5.1% severe and 5.1% small ratings) crowns without significant differences. Porcelain fractures had approximately 2 times higher odds (odd’s ratio=2.1) in patients with bruxism habits, with higher rates in mandibular regions than maxillary, in posterior regions than anteriorly located prostheses and in multiple-unit prostheses than single units. However, overbite, overjet, opposing type and angle classification showed no significant effect on the porcelain fractures.Conclusion: Implant-supported crowns showed 2 times more porcelain fractures than tooth-supported prostheses and the frequency of post-treatment complications was statistically higher in implant-compared to tooth-supported metal-ceramics. However, the difference of two systems was not statistically significant regarding porcelain fractures.