Extra-skeletal Ewing's sarcoma is among the rarest tumors in adults. The primary sites of the tumor dictates symptoms and signs, thus early treatments are compromised when more common tumors are lined up as differentials by the location. We present a case of a 35-year-old pregnant female who developed a renal Ewing sarcoma during pregnancy. A prior simple left kidney cyst in an ultrasound with no tumor signs was spotted. A month after her cesarean section she visited a doctor when she was sent and admitted for surgery with renal cell carcinoma as the primary diagnosis to the Firoozgar hospital. Histology confirmed the final diagnosis. To this end, she completed the standard chemotherapy for the renal Ewing sarcoma with pulmonary metastasis when she was re-evaluated for the general bone pain, diagnosed with multiple bone metastases, and ultimately approached her palliative care. She expired after 2 months. This study demonstrates: a gently progressive mass; palpable in late stages; introduced rise in mean corpuscular volume and lactate dehydrogenase with no drop in the hematocrit. In conclusion, any random parenchymal and/or cortical thickening in primary ultrasound and/or computed tomography demonstrating a cyst—whether displaying internal echo or not— with suggested signs should be furtherly evaluated.