Indeterminate colitis is only a partial diagnosis, which is provisional until sufficient information becomes available for a more precise diagnosis of either ulcerative colitis or Crohn's disease. As originally defined, i.e. based only on the pathological features in the colon resected for fulminant colitis, a few patients eventually developed Crohn's disease. If the term is used only after all available clinical and investigative evidence is considered, 'indeterminate colitis' behaves clinically like ulcerative colitis. This has important implications for pouch surgery.