['To evaluate commonalities in presentation and long-term efficacy of treatment by percutaneous nephrostolithotomy of matrix stones, a rare form of urinary calculi.', 'The clinical data of 9 consecutive patients with urinary matrix calculi in 11 kidneys treated at our institution between 1995 and 2007 were retrospectively reviewed.', 'The matrix component in all 11 kidneys was successfully treated with percutaneous nephrostolithotomy, with few complications. Among 8 patients (9 kidneys) with follow-up, none has had recurrence of matrix stones after a mean follow-up of 3.8 years. Along with previously known risk factors for matrix stones, such as urinary tract infections and renal insufficiency, we identified smoking as another possible risk factor. Long-term antimicrobial prophylaxis was used in only 1 patient and thus does not seem necessary for prevention of recurrence.'] Do the University of Michigan experience with percutaneous nephrostolithotomy for urinary matrix calculi?