Functional hyposplenism is a condition accompanying many diseases such as sickle cell disease, celiac disease, alcoholic liver disease, hepatic cirrhosis, lymphomas and autoimmune disorders. It is characterised mostly by defective immune responses against infectious agents, especially encapsulated organisms, since the spleen is thought to play an important role in the production and maturation of B-memory lymphocytes and other substances like opsonins, both of which are considered crucial elements of the immune system for fighting infections. It is also associated with thrombocytosis, which might lead to thromboembolic events. Functional hyposplenism is diagnosed by the presence of Howell-Jolly bodies and pitted erythrocytes in the peripheral blood smear, and by nuclear imaging modalities such as spleen scintigraphy with the use of Technetium-99m and/or spleen scintigraphy with the use of heat-damaged Technetium-99m labeled erythrocytes. Severe infections accompanying functional hyposplenism can lead to the overwhelming post infection syndrome, which can often be fatal. Identifying patients with functional hyposplenism is important because simple measures such as vaccination against common infective microorganisms (e.g. Streptococcus pneumonia, Neisseria meningitides and Haemophilous influenzae) and antibiotic therapy when needed are considered beneficial in diminishing the frequency and gravity of the infections accompanying the syndrome.