To summarize and update our current knowledge regarding adenomyosis diagnosis, prevalence, and symptoms. Systematic review of PubMed between January 1972 and April 2020. Search strategy included: "adenomyosis [MeSH Terms] AND (endometriosis[MeSH Term OR prevalence study [MeSH Terms] OR dysmenorrhea[Text Word] OR prevalence[Text Word] OR young adults [Text Word] OR adolesce* [Text Word] OR symptoms[Text Word] OR imaging diagnosis [Text Word] OR pathology[Text Word]. Articles published in English that addressed adenomyosis and discussed prevalence, diagnosis, and symptoms were included. Included articles described: pathology diagnosis, imaging, biopsy diagnosis, prevalence and age of onset, symptoms, and concomitant endometriosis. Sixteen articles were included in the qualitative analysis. The studies are heterogeneous when diagnosing adenomyosis with differing criteria, protocols, and patient populations. Prevalence estimates range from 20% to 88.8% in symptomatic women (average 30-35%) with most diagnosed between 32-38 years old. The correlation between imaging and pathology continues to evolve. As imaging advances, newer studies report younger symptomatic women are being diagnosed with adenomyosis based on both magnetic resonance imaging (MRI) and/or transvaginal ultrasound (TVUS). High rates of concomitant endometriosis create challenges when discerning the etiology of pelvic pain. Symptoms that are historically attributed to endometriosis may actually be caused by adenomyosis. Adenomyosis remains a challenge to identify, assess and research because of the lack of standardized diagnostic criteria, especially in women who wish to retain their uterus. As noninvasive diagnostics such as imaging and myometrial biopsies continue to improve, younger women with variable symptoms will likely create criteria for diagnosis with adenomyosis. The priority should be to create standardized histopathological and imaging diagnoses to gain deeper understandings of adenomyosis.