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 ≤ 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 and by Kistner and coauthors revealed differences among fecundability rates among the different categories (P ≤ 0.01); however, the system suggested by The American Fertility Society (AFS) revealed significant differences only if categories were combined (mild plus moderate versus severe plus extensive, P ≤ 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 ≤ 0.01).