An examination of a blood smear may be requested by physicians or initiated by laboratory staff as a diagnostic aid when a lymphoproliferative disorder or mononucleosis is suspected.¹ The classification of lymphocyte disorders is complex because there are various manifestations of these disorders.^2,3 Three major groups can be distinguished: reactive lymphocytosis, premalignant neoplastic disorders of lymphocytes and neoplastic disorders of lymphocytes.⁴ Lymphocyte disorders may be accompanied by abnormal lymphocyte morphology; therefore it is important to recognise and report abnormal lymphocytes, such as atypical lymphocytes and lymphoblasts. The ability of individual technicians, however, to recognise abnormal lymphocytes is consistently quite poor.⁵ There are no standardised definitions regarding the morphology of the various cells, and interpretation is based on individual experience and dependent on the availability of additional clinical information. Often, transitional forms between lymphocytes and plasma cells are seen in the blood of patients with viral infections. These cells are variously known as atypical lymphocytes, lymphocytoid plasma cells or plasmacytoid lymphocytes.⁶ The so-called atypical lymphocyte is a non-neoplastic lymphocyte seen in the peripheral blood, and appears to be a non-specific response to stress from a variety of disorders.⁷ Small lymphocytes become larger in size and become capable of dividing. These atypical lymphocytes …