Urinary incontinence in children can be originated mostly from urinary tract infections, but constipation, neurologic disorders, obstruction and tumors can also be considered among other causes. Pelvic tumors may present with back pain, bladder or bowel dysfunction. Ewing's sarcoma is among the small round-cell tumors of the childhood and potentially can arise from any part of the body. Here, we report an 11-year-old male presented with urinary incontinence and diagnosed as Ewing's sarcoma after 6 weeks' delay. Clinicians should suspect from pelvic tumors in the presence of urinary incontinence especially associated with low back pain.