Urinary doubly refractile lipid bodies (oval fat bodies) are observed most frequently in patients with heavy proteinuria resulting from glomerular disease. We observed doubly refractile lipid bodies (DRLB) in the urine sediment of 60% of 35 patients with autosomal dominant polycystic kidney disease (ADPKD). All patients had clinical courses typical of ADPKD, and none exhibited the features of a second, unrelated renal disease. DRLB in the urine were correlated with a urine dipstick protein reading exceeding trace. Age, sex, BP, and serum creatinine concentration were not associated with the presence of DRLB in the urine. Examination of cyst fluid obtained from kidneys of six ADPKD patients revealed DRLB in 80% of cyst fluid samples that contained degraded blood (so-called chocolate cysts). The DRLB in cyst fluid were morphologically indistinguishable from those observed in urine, and DRLB from both sources were stained with oil red O. We conclude that urinary DRLB are a clinical feature of ADPKD.