Chronic pelvic pain and endometriosis remain two of the most perplexing problems in gynecology. In some women with both conditions, endometriosis might not be the cause of their pain. The problem is determining when the pain is caused by endometriosis. On the basis of clinical studies, I suggest three criteria that should be met before attributing chronic pelvic pain to endometriosis. First, the pelvic pain should be cyclic because endometriosis is a hormonally responsive disease. Second, endometriosis should be diagnosed surgically to avoid overdiagnosing this condition. Finally, medical or surgical treatment of endometriosis should result in prolonged pain relief. Application of these evidence-based criteria reminds us that endometriosis often can be asymptomatic, even in some women with chronic pelvic pain. These criteria might help gynecologists determine the women for whom surgical therapy will resolve the pain; however, only prospective evaluation can determine their ultimate usefulness.