Immunodeficiency is a state in which the immune system's ability to fight infectious disease and cancer is compromised or entirely absent. Most cases of immunodeficiency are acquired ("secondary") due to extrinsic factors that affect the patient's immune system.

The cause of immunodeficiency varies depending on the nature of the disorder.

The cause can be either genetic or acquired by malnutrition and poor sanitary conditions.

Although there is no true discrimination to who this disease affects, the genes are passed from mother to child, and on occasion from father to child.

Available treatment falls into two modalities: treating infections and boosting the immune system.

Some deficiencies cause early mortality (before age one), others with or even without treatment are lifelong conditions.

Newer stem cell transplant technologies may lead to gene based treatments of debilitating and fatal genetic immune deficiencies.