Abstract: Spleen is an important organ of the reticuloendothelial system. It plays a crucial role in the immunological system of the body. Understanding the consequences and diagnosis of hyposlenic and asplenic states is essential. Splenectomy is performed for a variety of indications ranging from haematological conditions to trauma. Complications of splenectomy include surgical as well as immunological. Overwhelming post splenectomy infection is one of the most dreaded complication with high mortality. The physiological basis of immunological function of the spleen, hyposplenism and complications of splenectomy are presented in this paper.