The authors report a case of renal hemosiderosis in a 33 year old patient with mitral valve replacement with a Saint Jude Medical prosthesis. Chronic, well-tolerated hemolysis developed after surgery and a peri-prosthetic leak was demonstrated. Alteration of renal function and abnormalities on urinalysis led to renal biopsy which showed massive localised hemosiderosis, mainly in the interstitial tissues. Repeat mitral valve replacement led to a regression of the hemolysis. Significant hemolysis in patients with mechanical cardiac valves prostheses should lead to investigation of prosthetic valve function and, if dysfunction is demonstrated, the patient should be considered for reoperation because of the potential severity of renal complications.