BACKGROUND: Adenomyosis is a prevalent gynaecological disorder whose pathogenesis remains incompletely understood. Congenital Müllerian anomalies provide an informative in vivo model, since obstructive and non-obstructive variants impose spatially defined alterations of intrauterine pressure, myometrial architecture, and contractility. OBJECTIVES: To characterise adenomyosis localisation across Müllerian anomaly subtypes, assess concomitant endometriosis prevalence, and examine their topographic concordance with sites of uterine obstruction. SEARCH STRATEGY: PubMed/MEDLINE, Embase and Scopus were searched from inception to October 2025 using MeSH/Emtree and free-text terms for adenomyosis and congenital Müllerian anomalies, without date restrictions. SELECTION CRITERIA: Original case reports, case series, and observational studies in English explicitly describing the diagnostic modalities used for both conditions. DATA COLLECTION AND ANALYSIS: Two reviewers independently screened and extracted data; methodological quality was assessed with the Joanna Briggs Institute tools. Data were synthesised descriptively by malformation subtype, with case-by-case laterality analysis where individual patient-level data were available. MAIN RESULTS: Forty-two studies (135 patients) were included. Unicornuate uterus predominated (102/135, 75.6%). Among patients with directly reported localisation and a non-communicating functional rudimentary horn, adenomyosis involved the rudimentary horn in 10/12 cases (83.3%). In Robert's uterus, adenomyosis was ipsilateral to the blind hemicavity in 3/3 evaluable cases (100%). In Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, adenomyosis occurred in remnants lacking functional endometrium in 10/15 patients (66.7%). Concomitant endometriosis (43/134 evaluable patients, 32.1%) was most frequent in obstructive anomalies (Herlyn-Werner-Wunderlich syndrome (HWW) 3/5, 60.0%; Robert's uterus 2/4, 50.0%) and least frequent in septate uterus (0/2, 0%) and MRKH (2/15, 13.3%), localising ipsilateral to the obstruction in 9/10 (90.0%) reported obstructive cases. CONCLUSIONS: Adenomyosis preferentially involved structurally abnormal or obstructed uterine compartments. The endometriosis gradient was compatible with impaired menstrual efflux as a shared mechanical determinant. These findings derive from a low-quality evidence base and should therefore be regarded as hypothesis-generating. Prospective confirmation is required, although these findings may support increased clinical awareness in women with Müllerian anomalies, particularly obstructive variants.