Idiopathic CD4+ lymphocytopenia (ICL) is a rare medical syndrome in which the body has too few CD4+ T lymphocytes, which are a kind of white blood cell.

[7] The mandatory criteria for diagnosis of idiopathic CD4+ lymphocytopenia include:[8] A one-time finding of low CD4+ cells is usually associated with a recent infection and resolves on its own.

Fludarabine-based hematopoietic stem cell transplantation (HSCT) has shown to be a feasible treatment for ICL.

[10][non-primary source needed] In contrast to the CD4+ cell depletion caused by HIV, in general, patients with idiopathic CD4 lymphocytopenia have a good prognosis.

[3] The major risk to people with ICL is unexpected infections, including cryptococcus, atypical mycobacterial and Pneumocystis jiroveci pneumonia (PCP).