Adenomyosis is a benign uterine condition defined as the presence of endometrial glands and stroma within the myometrium. Unfortunately, its pathogenesis remains uncertain. The international Morphological Uterus Sonographic Assessment (MUSA) group has published a consensus on the ultrasound features of adenomyosis in 2015. Among different adenomyosis phenotype, focal adenomyosis is a heterogeneous group of different pathogenic, histopathological and clinical entities. By using the sonographic features different types of focal adenomyosis may be identified: 1) focal adenomyosis in the outer myometrium involving the serosa, which might have a strong correlation with deep infiltrating endometriosis; 2) the presence of a focal area of direct signs of adenomyosis in the inner myometrium, most likely through direct invasion from endometrial cells from the uterine cavity; 3) the presence of a focal area of direct signs (i.e., hyperechogenic islands with or without myometrial cysts) in the middle or outer myometrium. Most likely, this lesion is part of more diffuse disease; 4) A macro-cystic lesion in the myometrium without contact with the junctional zone of myometrium; 5) Accessory and cavitated uterine mass (ACUM) in the outer myometrium, which are suggested to be a continuum of congenital uterine anomalies. Some of these entities have also been described in MRI. The scope of the present opinion paper is to describe the different entities of focal adenomyosis leading to new insights of the impact of each of these entities on both clinical symptoms (e.g. pain, bleeding, subfertility) and management options. However, the proposed concept might need amendment and should be the object of future research.