Background: Immune complex deposition in the subepithelial zone of glomerular capillaries can lead to membranous glomerulopathy. Objective: To present the case of a 23-year-old man with X-linked agammaglobulinemia (XLA) who developed idiopathic membranous glomerulopathy while receiving intravenous immunoglobulin (IVIG). Methods: We performed an immunological workup, genetic testing, and a renal biopsy. Results: XLA was confirmed with less than 0.02% CD19+cells in the blood after sequence analysis revealed a nonfunctional BTK gene. The patient presented with microhematuria, which persisted for 3 years and spanned treatment with 5 different preparations of intravenous gammaglobulin. Immunohistochemistry revealed membranous glomerulopathy. Conclusion: Although endogenous serum immunoglobulin (Ig) production is severely impaired in XLA, rare B lymphocytes that have managed to mature can produce functional IgG antibodies. The pathogenic immune complexes could refl ect IVIG reacting with polymorphic autoantigens, an endogenous IgG-producing clone reacting with a common idiotype present in the IVIG, or both.