A 65-year-old man presented to our institution for workup of proteinuria. His serum creatinine level was 1.7 mg/dL (130 micromol/L), and he had proteinuria with protein of almost 5 g/24 h. Fabry disease was diagnosed by means of kidney biopsy and low serum and leukocyte levels of alpha-galactosidase A. Review of his history, family history, physical examinations, and diagnostic studies did not show other findings typical of this disease. His renal function continued to decline, and he eventually underwent a living unrelated renal transplantation 5 years later. Three years after transplantation, his creatinine level is 1.7 mg/dL (130 micromol/L), and corrected iothalamate clearance is 53 mL/min/1.73 m2 . Genetic studies showed that he has a novel missense mutation (M42L) in exon 1. Methionine at codon 42 is highly conserved in eukaryotic alpha-galactosidase A orthologues. This genotype predicts a minor misfolding of alpha-galactosidase A because of a small difference in hydrophobicity between methionine and leucine. His mutation resulted in a very low, but detectable, serum level of alpha-galactosidase A (0.002 U/L; normal range, 0.016 to 0.2 U/L). Cases of Fabry disease that present with predominantly renal manifestations are rare and require a high index of suspicion for diagnosis. Because treatment for Fabry disease recently has become available, it is important for clinicians to be aware of this disease and pursue the diagnosis in cases of otherwise unexplained renal dysfunction.