Malignant tumors of the spermatic cord are rare with primary neoplasms being mostly sarcomas. Adenocarcinomas of the spermatic cord are found extremely seldom and are predominantly metastases of extragonadal tumors. We present an asymptomatic 47-year-old patient who was referred to our clinic after a vasectomy had been performed and the histological examination had surprisingly shown adenocarcinoma of the left spermatic cord. Extensive laboratory analysis and diagnostic imaging did not demonstrate any testicular, spermatic cord, or extragonadal tumor. To exclude a mix-up of specimens, we performed DNA analysis. Microsatellite PCR clearly demonstrated the different origins of the tumor and the vasectomy specimen. Specimen mix-up or contamination may happen in any phase of surgical or pathological processing. In any case of clinical uncertainty concerning the identity of a tissue specimen, this possibility has to be taken into consideration. Microsatellite PCR can clearly identify the origin of tissue samples even on embedded material.