A 51-year-old woman complained of a periprosthetic effusion ten years after a breast prosthesis implantation. The effusion was aspirated and the seroma was sent for flow cytometry and immunohistochemical analysis to the laboratories of the University-Hospital of Padova. The analyses revealed the presence of a lymphoid population with an abnormal phenotype and morphology. All neoplastic cells were large cells with anaplastic morphology, they were CD30-positive and Anaplastic Lymphoma Kinase (ALK)-negative. By integrating the clinical-anamnestic data with laboratory data, a diagnosis of Breast Implant-Associated Anaplastic Large Cell Lymphoma (BIA-ALCL) was made. This is a rare type of non-Hodgkin lymphoma that affects women with breast implants. Since this lymphoma was recognized by the WHO in 2016, only a few cases of BIA-ALCL have been described. However, thanks to the diagnostic workup introduced by the National Comprehensive Cancer Network guidelines and applied by the University-Hospital of Padova, the diagnosis of a still little-known and extremely rare lymphoma was possible. [ABSTRACT FROM AUTHOR]