Obstructive urolithiasis, or more correctly phosphocrystalluria (since calculi rarely occur in the feline kidney or ureter), occurs quite often in the male domestic cat. The female cat seems to escape this problem because her urethra is wider nd more expansible. The male cat, however, has a relatively narrow penile urethra and fine urinary crystals may obstruct and pack this urethral canal. If this condition is left untreated death is the usual result.