Rationale: Simple renal cyst (SRC) is a benign disease. However, rarely renal cell carcinoma (RCC) may be raised at the wall of a preexisting SRC. We herein describe 2 unusual cases of RCC arising from the outer surface of the free wall of the renal cyst. Patient concerns: A 75-year-old female and a male were admitted to our department because of an asymptomatic renal cystic mass. Although the case history, preoperative imaging, and intraoperative examination of the cyst were carefully evaluated, no concerns were raised with respect to the underlying malignancy. Diagnosis: RCC of the clear cell type was diagnosed based on the histology and pathological examination. Interventions: With an initial diagnosis of SRC, the retroperitoneal laparoscopic de-roofing of the SRC was performed in both of the patients. When the diagnoses were confirmed 7days postoperative, both of them were readmitted to our department for a radical nephroureterectomy. Outcomes: The postoperative course was uneventful and the two patients did not undergo further chemotherapy. They are currently well and have no clinical or radiological signs of recurrence. Lessons: Such cases remind us that seemingly benign renal cysts may harbor underlying neoplasia. Further evaluation and periodical follow-up are also recommended on the management of those seemingly benign renal cysts.