In the examinations of the appraisal commission of Northern Rhine the third most frequent urologic errors are ascertained after surgical procedures. In order to prevent them, it is adequate to evaluate their causes.Urologic claims were examined that came before the appraisal commission for treatment errors of the Northern Rhine Physicians' Authority between 1975 and 2005. The results of the first 23 years were compared with those of the last 7 years. The judgment criteria were professional standards and required care.Ninety-five treatment errors were registered in 1975-2005. From 1975 to 1998 there were 60 such errors (2.6 per year) and from 1999 to 2005 there were 35 (5.0 per year). These errors concerned diagnosis in 14.7% of cases (mainly testicular torsion), indication in 7.5%, and explanations of the surgery in 2.1%. About half the cases (46.3%) applied to surgical technique, especially for injuries to the spermatic cord, urinary bladder, ureter, or urethra. In nearly one third of cases (29.4%), errors were found in postoperative care, concerning especially lesions of the spermatic cord and ureter.There is considerable risk of misjudging or even causing urologic disorders in abdominal and vascular surgery. This applies most strongly to diagnosis, above all for testicular torsion. Hernia surgery and colon resection are the treatments leading to the highest number of injuries to testicular vessels, ureter, bladder, and/or urethra. Such occurrences cannot be tolerated if they can be avoided or, if unavoidable, not recognized promptly and adequately managed.