Idiopathic CD4⁺ T lymphocytopenia (ICL) is defined as a CD4⁺ T‐cell count <0·3 × 10⁹/l or <20% of the total T‐cell count on two occasions in the absence of any immunodeficiency disorder or therapy associated with reduced CD4⁺ T‐cell count. Although several mechanisms of ICL have been reported, the pathophysiology is still largely unknown. This case report describes a patient who presented with cryptococcal meningitis and was subsequently discovered to meet the criteria for ICL. Flow cytometric analysis of the patient's peripheral blood mononuclear cells revealed antibodies coating a much larger proportion of his CD4⁺ T cells (33·61%) than the CD4⁺ T cells of normal donors (3·94 ± 1·77%). The reasons behind the development of these autoantibodies are explored.