BACKGROUND: Primary anaplastic large-cell lymphoma (ALCL) occurring in women with breast implants is very rare. It is usually described as tumor cells infiltrating the periprosthetic capsule. These are most often revealed by a periprosthetic recurrent isolated effusion (seroma cavity), occurring late after implantation of the prosthesis. ALCL is more rarely a tumor or periprosthetic capsular contracture. CASE: We report a 66-year-old woman, initially diagnosed by cytological examination of breast effusion, in whom ALCL appeared two and a half months after the removal of a ruptured implant. Repeated biopsies of the periprosthetic capsule performed in parallel showed fibrous tissue, without tumor proliferation. Only meticulous histological examination of the total capsulectomy identified tumor cells as a thin and discontinuous layer along the inner surface of the capsule without capsular invasion. CONCLUSION: Awareness of the histological pattern of this new clinical entity is important. A total capsulectomy with a good sampling for microscopic examination should be conducted for any suspicion of breast implant-associated ALCL. Cytology-histology correlation is essential.