Selective progesterone receptor modulators may have a role in the treatment of endometriosis. The aim of this report is to review the effect of ulipristal acetate (UPA) on endometriosis lesions and symptoms in women treated prior to surgery. A pathology review of eutopic endometrium and endometriotic lesions was conducted by two gynecologic pathologists. The main outcome measures reported are pain reduction, amenorrhea, and pathologic progesterone receptor modulator-associated endometrial changes (PAECs). Overall, fifteen women with endometriosis received UPA over a 27-month study period. UPA was administered in an intermittent fashion in the majority of patients while 27% of patients had continuous treatment, between 6 and 24 months. Eleven (73%) patients reported amenorrhea on UPA and 11 (92%) of 12 patients with pain reported pain reduction or resolution. Fourteen patients (93%) proceeded with surgical management. Thirteen (93%) patients underwent excision of suspected endometriosis at surgery. Twelve cases (86%) had concurrent eutopic endometrium specimens and PAEC was identified in 58% (n = 7). Among the 14 cases that underwent surgery, a total of 49 extraovarian sites were sampled. Endometriosis was definitively identified in 31 (63%) of these sites. Three cases (21%) showed morphologic features similar to PAEC within foci of endometriosis. All cases of PAEC-like features in endometriosis also had PAEC in the endometrium. These patients had all noted pain reduction and amenorrhea preoperatively. In conclusion, PAECs may be found in endometriosis lesions in patients treated with UPA. Further prospective investigation is required to evaluate the efficacy and safety of SPRMs in women with endometriosis.