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The aim of this study was to analyze implant failure, causes, time of failure, and cluster behavior of implant failure among patients referred to a private surgical center.All failed implants placed during the years 1997–2004 were analyzed. Data collected included age, gender, smoking habits, implant type and dimensions, timing of implantation (immediate or nonimmediate), time to failure, and failure causes.Overall, 99 of the 3609 implants placed between the years 1997 and 2004 failed in 61 patients resulting in a 97.3% survival rate. Patients with implant failure ranged in age from 21 to 78 years (average 54 years); 34% were men, 66% women; smoking was reported by 32.8%, pastsmoking 16.4%; time from implant placement to failure ranged from 1 to 99 months (average 24 months, SD = 24.8). Common causes for implant removal were bone loss and/or inflammation (52.5%), and implant mobility (43.4%). Cluster behavior (ie, more than one implant failure per patient, not necessarily in the same area or quadrant) was shown in one-third (32.8%) of the patients in which 56.6% of all failures were found. This cluster pattern was evident in both the surgical and prosthetic phase failures.There is a higher probability for a cluster pattern among patients with implant failure. Common signs for failure are implant mobility (surgical phase) and infection and marginal bone loss (prosthetic phase).