Obesity is a common problem in the western European countries. Since the association between obesity and the emergence of gonarthrosis is approved, it is more important to gain reliable information about this patient group. The aim of the present retrospective study is to evaluate clinical outcomes of German obese patients after total knee arthroplasty (TKA). Between 2001 and 2009 a total of 199 patients with 230 TKA were included in the present study. The collective was divided into four groups in relation to their Body-Mass-Index (BMI); group 1: BMI < 25 kg/m2, n = 24; group 2: BMI 25-30 kg/m2, n = 80, group 3: BMI 30-40 kg/m2, n = 109; group 4: BMI> 40 kg/m2, n = 17. Clinical outcome measurement was scored postoperatively using the knee society score (KSS), hospital for special surgery score (HSS) and the visual analogue scale (VAS). Furthermore complications and subjective patient satisfaction were noted. We did not detect any significant differences in the clinical scores between the BMI-subgroups. However we measured statistically significant worse results in case of infection and instability in all BMI subgroups (p> 0.01). While infection and instability may have a negative influence for the clinical outcome, we did not detect any significant correlation between obesity and exiting complications. Obesity has no significant correlation to influence the outcome after TKA implantation negatively.