Attygalle AD, Zamo A, Fend F, et al. - In 2018, for Haematopathology/Society of Hematopathology, the focus of the 3rd session of the bone marrow (BM) workshop of the 19th meeting of the European Association in Edinburgh was on diagnostic challenges posed by challenges in clarifying borders between overlapping primary bone marrow T-cell and T/NK lymphoproliferation and the limitations of applying existing defining criteria related to nodal-type T-cell lymphomas and extranodal T/NK cell lymphoproliferation to isolated involvement or initial presentation in the BM. It is demonstrated that the diagnosis and classification of T-cell lymphomas and NK/T-cell lymphomas based on bone marrow (BM) biopsy findings alone are challenging and controversial. Primary presentation in the marrow happens in those lymphomas where it is a main and common site of involvement and rare examples of nodal-type T-cell lymphomas and extranodal T-cell and NK/T-cell lymphomas with isolated marrow involvement or where presentation in the marrow precedes that of extramedullary sites.