A homogeneous group of 214 infertile women with endometriosis treated at the Johns Hopkins Hospital from 1960 to 1979 received conservative surgery as the sole therapeutic modality. Among this group, 115 patients (54%) conceived following surgery; of these conceptions, 109 resulted in a living child. Among 49 patients with secondary infertility, the spontaneous abortion rate was reduced from 49% to 20% after conservative surgery (P less than or equal to 0.01). Three contemporary classification systems were utilized to categorize patients according to the sites and amount of endometriosis at the time of conservative surgery. Those systems suggested by Buttram (Fertil Steril 30:240, 1978) and by Kistner and coauthors (Fertil Steril 28:108, 1977) revealed differences among fecundability rates among the different categories (P less than or equal to 0.01); however, the system suggested by The American Fertility Society (AFS) (Fertil Steril 32:633, 1979) revealed significant differences only if categories were combined (mild plus moderate versus severe plus extensive, P less than or equal to 0.05). Nevertheless, the AFS system revealed that pregnancy success was significantly reduced if an ovarian endometrioma was greater than 3 cm or had ruptured (P less than or equal to 0.01).