Background and objectives: The treatment of edentulousness with dental implants is usual a procedure in most of the western countries. From the published data it is well known that previous data upon periodontal disease and smoking might lead to the more frequent failure of implanto-prosthetic therapy. Systemic diseases such as diabetes mellitus, atherosclerosis, cardiovascular disorders, thyroid disease, osteoporosis, chemotherapy and radiotherapy in the head and neck area have been proposed as a factors that might contribute to the failure of implanto-prosthetic therapy. Furthermore, implant characteristics such as type, diameter and length of implant as well as its connection with prosthetic suprastructure (screw retained or cemented one) migh influence the success of implanto-prosthetic therapy. Also, surgical technique and placement in the upper or lower jaw might additionally influence the success of impalnto-prosthetic therapy. It is estimated that such a treatment is highly successful, although there is still a need for studies which would include local and systemic factors on big populations in order to detect potential failures. The aim of this study was to analyze whether the previous presence of periodontal disease, oral hygiene status i.e. bleeding on probing (BOP) and full mouth plaque index (FMPI), smoking, systemic diseases as well as implant characteristics (type, length, shape) and type of connection with prosthetic suprastructure affect implant-prosthetic failure. Methods: Data from 670 patients were retrieved in whom 1260 dental implants were installed and who were followed in the course of at least five to ten years. All patients were treated in the private clinic in Zagreb by one experienced clinican. In every participant anamnestic data regarding age, gender, smoking habit, previous data upon periodontal disease, systemic diseases such as diabetes mellitus, atherosclerosis etc. were registered. In every patient, type of implant (lenght, diameter and shape) was registered as well as place in the bone where was installed as well as type of retention of the prosthetic suprastructure (cemented/screw retained). Plaq index of the full mouth was assesed together with bleeding on probing. The participants were called for recall after five years in order to determine whether periimplantitis was present or unsuccesful osseointegration nas occurred. Data were analysed using Medcalc (v11.4). Categorical data were analysed by the Chi-square test. Continued variables (age, BOP, FMPI) were not normally distributed, therefore the non-paramteric Mann-Whitney test was used. P values lower than 0.05 were significant. The influence of local and systemic factors on the success of implanto-prosthetic therapy was assesed by multiple logistic regression analysis. Loss of implants was dependent variable while age, smoking, previous data upon periodontal disease, type, length and diameter of implants, type of retention with prosthetic suprastructure and systemic diseases were independent variables. Results: Forty five patients had systemic diseases 45 pacijenata (6.7%), and diabetes mellitus was the most common one among them (n=35), followed by atherosclerosi (n=8), diabetes and atherosclerosis (n=5), diabetes mellitus type 1 (n=3), lymphoma (n=1) and hepatitis C (n=1). One third of the patients were smokers (33.4%). Most of the patients were 41-60 years old, mean age 53.9%. All patients were treated during the period of the year 2008 till the year 2012. therefore the obtained data could be retrieved for at least five years. One hundred and 70 patients had periodontal disease, while 500 patients were without periodontal disease. Of 670 patients, 628 patients had only one procedure. The number of installed implants was one in 333 patients, i.e. more than one in 337 patients. Nine implants were lost during the period of five years. There were no differences regarding the type of implant or type of connection to prosthetic suprastructure. However, most of these patients had a periodontal disease. There were no significant differences in dental implant failure between smokers and non-smokers and between patients with systemic diseases and those without systemic diseases. Furthermore, the results of this study showed that implant type (straight vs tapered) and type of connection with prosthetic suprastructure (cemented or screw retained) did not affect BOP and FMPI. In smokers, significant improvement of BOP and FMPI was noticed. Initially, the smokers had significantly worse BOP (0,0037) when compared to the non-smokers, however, there were no differences regarding FMPI (p=0,4218) between the two groups. In patients with periodontal disease, an improvement of BOP and FMPI was seen after 5 years of followup and no significant differences were found when compared to patients without periodontal disease. There were no signficant differences in BOP and FMPI between patients with diabetes and those without diabetes after five years of follow-up. Atherosclerosis had a negatively significant effect of BOP, but without FMPI after five years of follow-up. Conclusion: We might conclude that periodontal disease had significant impact on the implant-prosthetic therapy.