The recurrence of pelvic endometriosis some time after the initial treatment is a common finding in clinical practice. When symptoms of endometriosis reappear several months after treatment, it is difficult to distinguish between recurrence and persistence of the disease. In this review, the current hypotheses about the biological basis of endometriosis recurrence/persistence are discussed. The results of several clinical trials estimating the recurrence rate of endometriosis after medical, surgical, and combined treatments are presented. In addition, a critical analysis of the tools available for the diagnosis of recurrent endometriosis is made, and some therapeutic options to treat recurrent endometriosis are discussed with recommendations for their use.