Blood in the urine may or may not be accompanied by pain, but it is always abnormal and should be further investigated by a healthcare professional. Painful blood in the urine can be caused by a number of disorders, including infections and stones in the urinary tract. Painless blood in the urine can also be due to many causes, including cancer. Blood in the urine is also referred to as hematuria. Visible blood in the urine is referred to as gross hematuria, while blood in the urine that is not visible to the naked eye is referred to as microscopic hematuria.

Source: http://www.rxlist.com