Background: Chronic pelvic pain is a debilitating condition affecting quality of life. Endometriosis is one of the leading causes of CPP, but recent studies highlighted the role of interstitial cystitis/bladder pain syndrome (IC/PBS) in causing CPP. Only some studies addressed the coexistence between these two conditions, which seems more frequent than what is supposed, leading to diagnostic delays and unnecessary surgeries. This systematic review aimed to evaluate the estimate of the coexistence of endometriosis and IC/PBS. Methods: We performed a systematic review of the literature indexed on PubMed, Scopus, ISI Web of Science, and Cochrane using a combination of keywords and text words represented by “painful bladder syndrome”, “endometriosis”, “interstitial cystitis”, “bladder pain syndrome”. We performed a meta-analysis of the results. Results: Meta-analysis shows that the coexistence of endometriosis and IC/PBS in women with CPP ranges between 15,5-78,3%, which is higher than the prevalence of IC/PBS in the general population. Conclusions: Women with CPP need a multidisciplinary approach and a referral to centers with specific expertise. In cases of endometriosis unresponsive to treatment, other reasons for CPP need to be ruled out, above all in women not responsive to treatment.