Predictors of clinical significance of residual fragments after extracorporeal shockwave lithotripsy for renal stones. 
To determine the predictors of the clinical outcome of residual fragments after extracorporeal shockwave lithotripsy (SWL).  During the last 10 years, residual fragments < or =5 mm were present in 99 male and 55 female patients (mean age 43.1 years) for >3 months after SWL for renal stones.  Follow-up with history, urine examination, and non-contrast CT scanning was carried out every 6 months or when symptoms developed.  Clinically insignificant residual fragments were diagnosed in patients who became stone free or had asymptomatic fragments of the same size during follow-up.  A clinically significant outcome was considered to have occurred in patients requiring secondary intervention for regrowth of the fragments or medical treatment for frequent symptomatic episodes.  Univariate (Kaplan-Meier) and multivariate (Cox-regression) analyses were performed to determine significant predictors of the outcome.  The mean follow-up was 31 months (range 6-80 months).  Stone-free status, regrowth of fragments, and persistence of fragments of the same size were present in 21 (13.6%), 52 (33.8%), and 81 (52.6%) patients, respectively.  A clinically significant outcome was documented in 75 patients (48.7%) as percutaneous nephrolithotomy was needed in 2, repeat SWL in 50, and medical treatment for symptomatic episodes in 23 patients.  Significant independent predictors of a clinically significant outcome were fragment size > or =4 mm and history of recurrent stone disease (P < 0.001).  The term "clinically insignificant residual fragments" is not appropriate for all patients with post-SWL fragments, as 48.7% of patients had fragments that became clinically significant.  Fragments of 4 to 5 mm and recurrent stone disease predicted clinical significance.