We report here on an 11-year-old Japanese girl who was found to have proteinuria by routine mass screening urinalysis for school children, and who developed systemic lupus erythematosus (SLE) 21 months later. The initial renal biopsy, performed 3 months after the first visit to Tokyo Medical University Kasumigaura Hospital (TMUKH), revealed membranous glomerulonephritis. In an immunofluorescent study, IgG was the only positive immunoglobulin found. A "full-house" immunofluorescence glomerulopathy, well known as a predictive finding for lupus nephritis, was not detected. Endothelial tubuloreticular inclusions (ETI) were found by electron microscopy. Because the diagnosis of SLE was not established clinically and serologically, the patient was followed every 3 months without drugs. Her urinary findings returned to normal within 18 months. Three months after the last visit, she was sent to Tsukuba University Hospital (TUH) for fever, arthralgia, dyspnea and butterfly rash. She was diagnosed as having SLE, pleuritis, and pericarditis. Although she was treated with methylpredonisolone and oral prednisolone, she developed cardiac tamponade on the 12th day of admission during the course of pneumococcal septicemia. Finally, she was treated successfully with surgical procedures, antibiotics and oral prednisolone and was discharged. We conclude that ETI is a more significant early sign of SLE than "full-house" immmunofluorescence glomerulopathy, especially in pediatric cases.