Isolated deposition of the third component of complement (C3) in the renal arterioles has been noted on biopsy specimens in patients with hematuria. This entity is of little known significance and reports of this finding in pediatric patients with hematuria are rare. We reviewed the clinical histories and biopsies of 17 children with hematuria and vascular C3 deposition on biopsy at Texas Children's Hospital over an 14-year period. The mean age of presentation was 10.8 (range 4.5-16.6) years with a male preponderance (71%). Family history for hematuria was positive in 6 of 17 patients (35%). Light microscopy was normal or showed only minor abnormalities. Immunofluorescence was negative for IgA and IgG in all patients. Seven patients (41.1%) were noted to have diffuse or focally thin basement membranes on electron microscopy in addition to positive C3 immunofluorescence. The mean follow-up time was 23.8 months, during which 2 of 17 patients (12%) developed worsening proteinuria. The etiopathogenesis of this condition remains unclear, but an underlying immunological process cannot be ruled out. It is possible that this condition represents a stage of an acute glomerulonephritis. Clinical follow-up of these patients is warranted, as the long-term prognosis remains unclear.