What is the causes of blood in the urine?

Many, usually benign: Bladder infection (hemorrhagic cystitis), kidney or bladder stone, interstitial cystitis, glomerulonephritis ( type of kidney disease), bleeding blood vessel abnormality, malignancies (eg cancer) of bladder, kidney, prostate or urethra or can be benign microscopic hematuria (sometimes familial). But rule of thumb is that it signifies possible cancer unless proven to the contrary.