To estimate the clinical effectiveness of in vitro fertilization treatment in patients with minimal or mild endometriosis (stages I and II) in comparison to the patients with tubal infertility in terms of fertilization, pregnancy and livebirth rates. Retrospective analysis of the outcome of IVF-ET in 612 cycles of the patients with endometriosis (389 stimulated with HMG/HCG and 223 co-treated with GnRH-a) and in 7,339 cycles of the patients with tubal infertility (5,520 stimulated with HMG/HCG and 1,819 co-treated with GnRH-a). RESULLTS: Regardless of the type of ovarian stimulation, the fertilization rate per treated cycle was practically the same in both groups (endometriosis 81.4% vs tubal infertility 84.2%; p = 0.07). However, in the endometriosis group the pregnancy rate was higher (25.3% vs 18.9%; p = 0.000), and so was the livebirth rate (19.0% vs 14.2%; p = 0.003). Considering the type of ovarian stimulation, the fertilization rate in the endometriosis group was almost the same in the HMG/HCG (81.2%) and in the GnRH-a co-treated cycles (81.6%), and did not differ from that in the tubal infertility group (83.6% in the HMG/HCG vs 85.9% in the GnRH-a cycles). In the GnRH-a co-treated cycles the pregnancy rate and the livebirth rate were not significantly higher in the endometriosis group than in the tubal infertility group (27% and 20.2% vs 22.2% and 17.5%). In the HMG/HCG stimulated cycles the pregnancy rate was significantly higher in the endometriosis than in the tubal infertility group (24.3% vs 17.7%; p = 0.004), and so was the livebirth rate (18.4% vs 13.0%; p = 0.008). In patients with minimal or mild endometriosis the IVF-ET procedure is at least as effective as in patients with tubal infertility.