Adenomyosis remains challenging to diagnose due to its unclear pathogenesis and clinical overlap with conditions such as endometriosis and uterine fibroids. While non-invasive imaging techniques like transvaginal ultrasound and magnetic resonance imaging have improved adenomyosis detection, histopathological examination remains the gold standard. As this typically requires hysterectomy, it limits fertility-preserving diagnostic options. Therefore, the search for potential biomarkers is essential to improve the diagnosis of adenomyosis. This review summarises current evidence on genomic, transcriptomic, proteomic, metabolomic and microbiome biomarkers identified using conventional molecular techniques and high-throughput multi-omics approaches in eutopic endometrium, blood, urine, faeces, cervicovaginal lavage and vaginal swab samples with potential clinical applicability, enhancing diagnostic accuracy, and enabling early detection and monitoring. In addition, describing adenomyosis biomarkers may enhance the understanding of adenomyosis pathogenesis and help identify new therapeutic approaches. Although numerous candidate biomarkers have shown promising results (e.g. STEAP1, TOMM20, GLT8D2, and NME5, hsa_circ_008959/hsa-miR-124-3p/SLC15A4 + VAS score, miR-92a-3p or Weissella confusa, and Lactobacillus zeae), the current evidence remains insufficient for their implementation in routine clinical practice owing to the lack of external validation, standardised methodologies, and large multicentre studies.