There is a lack of an international consensus on adenomyosis classification that is useful for clinical practice and research. This article reviews advancements in the classification of adenomyosis, and the existing limitations. We collected a literature search from PubMed and Embase database up to March 2019. The proposed adenomyosis classification is based on magnetic resonance imaging and clinically relevant parameters. Adenomyosis is not a disease of homogeneity but is composed of multiple heterogeneous subtypes. Adenomyosis represents a spectrum of lesions, ranging from increased thickness of the junctional zone to focal or diffuse lesions involving the entire uterine wall. Potentially important parameters to be included in the classification could be affected area (internal or external adenomyosis), pattern (focal or diffuse), size or volume (myometrial involvement <1/3, <2/3, or >2/3 of uterine wall), concomitant pathologies (none, peritoneal endometriosis, ovarian endometrioma, deep infiltrating endometriosis, uterine fibroids, or others) and localization (anterior, posterior, left lateral, right lateral, or fundal). We propose a simplified classification system to monitor symptom severity against morphological types or extent of adenomyosis using the combination of previously published classifications as a starting point. More studies are needed to investigate whether this classification represents a useful tool for disease assessment in clinical practice and research.© 2020 S. Karger AG, Basel.