To evaluate the pre-existing renal lesions (PERL) found incidentally during evaluation for blunt renal trauma, determine their importance, and suggest guidelines for effective management, including conservative treatment, we reviewed 180 patients who were hospitalized with blunt renal trauma between 1992 and 2008. Thirty of the 180 (16.6%) patients had PERL, which had been undiagnosed. The mean follow-up was 5 years (range 1-9 years). There were 24 men and 6 women with a mean age of 30 years (range 14-80 years). The most common cause of blunt renal injuries was falls and sports. Renal stones were present in 14 patients, pelvi-ureteric junction obstruction in 12, ectopic kidney in two, and megaureter and renal cyst in one case each. Ureteral stenting was used in four cases, and early nephrectomy was required in the other four. Fourteen patients underwent surgery for the PERL and not trauma, with a pyeloplasty in eight cases, partial nephrectomy in three cases, percutaneous nephrololithotomy in two cases, and ureteroneocystostomy in one case. In our study, the conservative treatment was possible in 73% of cases. We believe the published data support increasing conservative attempts in the hemodynamically stable patient.