Updated project metadata. Autosomal dominant polycystic kidney disease (ADPKD) is a common cause of ESRD. Affected individuals inherit a defective copy of either the PKD1 or PKD2 gene, encoding the proteins polycystin?1 (PC1) or polycystin?2 (PC2) respectively. PC1 and PC2 are secreted on urinary exosome?like vesicles (ELVs) (100nm diameter vesicles), where PC1 is present in a cleaved form and may be complexed with PC2. Label free quantitative proteomic studies of urine ELVs in an initial discovery cohort (13 PKD1 and 18 Normals), revealed that of 2008 ELV proteins, nine (0.32%) showed a statistically significant difference between PKD1 and normals at a p<0.025. PC1 was reduced to 54% of the normal level (p<0.02) and PC2 reduced to 53% (p<0.001). TMEM2, a protein with homology to fibrocystin, the product of the polycystic hepatic and kidney disease (PKHD1) gene, is increased 2.1 fold (p<0.025). The PC1/TMEM2 ratio correlated inversely with height adjusted total kidney volume (HtTKV) in the discovery cohort and the ratio of PC1/TMEM2 or PC2/TMEM2 could be used to distinguish PKD1 from normals in a confirmation cohort. In summary, this study suggests that a test based on the urine exosomal PC1/TMEM2 or PC2/TMEM2 ratio may have utility in the diagnosis and perhaps monitoring of PKD1.