Abstract: Type 1 diabetes mellitus is characterized by loss of pancreatic insulin-producing beta cells, resulting in insulin deficiency. The usual cause of this beta cell loss is autoimmune destruction. Coxsackie virus has been detected in human pancreatic beta cells and causes insulitis. This non-destructive islet inflammation does not itself cause diabetes, but this disease will occur if viral infection is followed by a separate autoimmune response. The insulitis is mediated mainly by natural killer cells. Islets from coxsackie virus positive samples displayed reduced insulin secretion in response to glucose and other secretagogues. Virus extracted from positive islets was able to infect beta cells from human islets of non-diabetic donors, causing viral inclusions and signs of pyknosis.