Background: Interleukin-1 (IL-1) is a proinflammatory cytokine that plays an important role in the pathogenesis of periodontitis, and so it might be useful to detect high-risk cases of peri-implantitis. It has been reported that IL-1 polymorphisms and smoking habit have a synergic effect, increasing the incidence of peri-implantitis. The aim of the present study was to evaluate the relationship between IL-1 gene polymorphisms and peri-implantitis in smoking patients. Material and Methods: A case-control study was performed in 27 patients with peri-implantitis and 27 patients with healthy implants. All patients included were smokers. IL-1A-C889T, IL-1B+C3953T and IL-1RN+T2018C were identified by polymerase chain reaction (PCR) amplification in order to establish a relation between these variables and the presence of peri-implantitis. A bivariate analysis was performed and odds-ratio (OR) were calculated. Results: The incidence of peri-implantitis was significantly higher in patients with previous history of periodontitis ( p =0.024; OR=10.9). Both groups were similar regarding IL-1A-C889T, IL-1B+C3953T and IL-1RN+T2018C genotypes. No increased risk in heavy smokers with IL-1 polymorphism was found. Conclusions: IL-1 genotypes do not seem to be good predictors of peri-implantitis in the great majority of smoking patients. Furthermore, no synergic effect was found between IL-1 genotypes and heavy smokers. Patients with a previous history of periodontitis were more prone to peri-implantitis.