The simple nephrectomy is usually performed in daily urology practice for the non-functioning kidney. The aim of this study is to determine the incidental malignancy rate of the patients who underwent nephrectomy procedure. In total, 258 patients were included in the study. The patients who underwent simple nephrectomy and diagnosed as renal tumor between January 2003 and March 2016 for the non-functioning kidney at our department were recorded. There were 258 patients in this study. Of these patients;123 were male and 134 were female patients. The mean age of the patients’ was 52.33+17.63 years. The presence of stone formation was detected in 92 patients (35.65%). The renal malignancy was reported in 9 patients.Among the patients with malignancy; 2 patients were female and 7 patients were male. The mean age of the patients was 54.77+8.81 years. The pathological examination revealed that 6 patients were transitional cell carcinoma (TCC) of the renal pelvis, 2 patients were renal cell carcinoma, one patient was cystic nephroma. Interestingly, nephrolithiasis was detected only in one patient. The prevalence of all malignancy and the malignant tumor was 3.48% and 3.10% in this study. The final pathology showed that there is a risk of malignancy fort he patients with the non-functioning kidney. The clinicians should be aware that the patient may be diagnosed as renal tumor after pathological examination.