Background & objectives: Women with endometriosis often need in vitro fertilization (IVF) to concieve. There are conflicting data on the results of IVF in patients with endometriosis. This study was undertaken to elucidate the influence of endometriosis on IVF outcome to give the best counselling for infertile patient with this problem. Methods: The outcome measures in 78 patients with surgically confirmed endometriosis were compared with 157 patients with tubal factor infertility, all of whom have undergone IVF. The groups were matched for age and follicle stimulating hormone (FSH) levels. Outcome measures included number of follicles, number of ocytes, peak oestradiol (E2) concentrations and mean number of ampoules of gonadotropins. Cumulative pregnancy, miscarriage and live birth rates were calculated in both the groups. Results: Higher cancelation rates, higher total gonadotropin requirements, lower peak E2 levels and lower oocyte yield were found in women with endometriosis and previous surgery compared with those with tubal factor infertility. However, no differences were found in fertilization, implantation, pregnancy, miscarriage, multiple births and delivery rates between the endometriosis and tubal factor infertility groups. Interpretation & conclusions: The present findings showed that women with endometriosis and previous surgery responded less well to gonadotropins during ovarian stimulation and hence the cost of treatment to achieve pregnancy was higher in this group compared with those with tubal factor infertility. However, the outcome of IVF treatment in patients with endometriosis was as good as in women with tubal factor infertility.