SummaryWe present the case of a 39-year-old white man with a Myobacterium aviumintracellulare pulmonary infection found to have a CD4+ count of 172 cells/ mm 3 and diagnosed subsequently with idiopathic CD4 + lymphopenia (ICL). After receiving clathromycin for 4 months with minimal improvement, the patient was started on pegylated subcutaneous interleukin (IL)-2 at 600 000 units daily. Later, he received incrementally higher pegylated IL-2 doses until he reached a maintenance dose 3 months later of 11 million units weekly divided into three equal doses. After 5 months of therapy, the patient's chronic cough resolved completely, sputum cultures became negative for Myobacterium avium-intracellulare and the CD4 + T cell count increased to 553 cells/mm 3 . After 35 months of well-tolerated IL-2 treatments and no recurrence of any opportunistic infections, IL-2 treatment was stopped. CD4 + counts 6 and 9 months after discontinuing IL-2 treatment were 596 and 378 cells/mm 3 respectively, and he remains asymptomatic. This report supports IL-2 treatment for ICL-associated opportunistic infections as a safe and potentially efficacious treatment option, especially when combined with more traditional treatment regimens.