PURPOSE To correlate preoperative serum cancer antigen 125 (Ca-125) levels and laparoscopic findings in women with pelvic pain symptoms suggestive of endometriosis. METHODS A retrospective study was conducted including all women with pelvic pain symptoms suspected for endometriosis operated by laparoscopy from January 2010 to March 2013. Patients were divided into 2 groups according to preoperative Ca-125 level (<35 U/mL and ≥ 35 U/mL). Subsequently, patients with ovarian endometriomas were excluded and a further analysis was conducted again according to the preoperative Ca-125 level. The following parameters were compared between groups: presence of ovarian endometrioma, presence and number of deep infiltrating endometriosis (DIE) lesions and American Society for Reproductive Medicine score. The statistical analysis was performed with Statistica version 8.0, using the Fisher exact test, Student's t-test and Mann-Whitney test, when needed. A p value of <0.05 was considered to be statistically significant. RESULTS During the study period, a total of 350 women were submitted to laparoscopic treatment of endometriosis. One hundred thirty patients (37.1%) had Ca-125 ≥ 35 U/mL and 220 (62.9%) had Ca-12<35 U/mL. The presence of ovarian endometriomas (47.7 versus 15.9%), DIE lesions (99.6 versus 78.6%) and intestinal DIE lesions (60 versus 30.9%) was more frequent, and the AFSr score was higher (34 versus 6) in the former group. In the second analysis, excluding the patients with ovarian endometriomas (≥ 35 U/mL=68 patients and <35 U/mL=185 patients), similar results were obtained. The presence of DIE lesions (91.2 versus 76.2%), intestinal DIE lesions (63.2 versus 25.4%), bladder DIE lesions (20.6 versus 4.8%) and ureteral DIE lesions (7.3 versus 1.6%) was more frequent, and the AFSr score was higher (10 versus 6) in the Ca-125 ≥ 35 U/mL group. CONCLUSIONS Investigation for DIE is mandatory in women with pelvic pain symptoms suggestive of endometriosis with a preoperative Ca-125 level ≥ 35 U/mL, especially when an ovarian endometrioma is not present.