The association of idopathic nephrotic syndrome (INS) with tubular dysfunction is uncommon. The authors report on 9 pediatric cases (6 girls and 3 boys). All the patients (age 12 to 48 months) presented initially with a pure INS. The syndrome was clinically severe and either initially or secondarily resistant to steroid and immunosuppressive therapy. In 6 cases initial renal biopsies showed minimal glomerular lesions and in one case, segmental and focal hyalinization was observed. Symptoms of tubular insufficiency appeared progressively and included: proximal and distal hyperchloremic acidosis (9/9 cases), renal glycosuria (9/9 cases), hypokalemia with hyperkaluria (7/9 cases), hypohposphatemia (4/9 cases), global hyperaminoaciduria (4/9 cases), tubular proteinura (2/9 cases). Control of water and electrolyte balance was difficult. The urinary concentration of fibrinogen breakdown products was very high throughout the course of the disease. In all cases, anemia preceded the inevitable alteration of glomerular filtration which resulted in four cases of terminal renal failure after an average evolution of 2 to 3 years. Renal biopsies during the later stages of evolution demonstrated five cases of glomerular hyalinization with interstitial fibrosis associated in 3 cases with histiocytic infiltration. Immunologic studies were negative. The authors discuss the physiopathologic aspects of the disease including the possibility of thrombosis of intrarenal veins and compare their observations with those of Royer et al. [1963].