Reference is made to 2 cases of fatal liver failure following jejuno-ileal by-pass for obesity, in which necropsy shown micronodular and the rarer fragmentary necrosis, in addition to serious steatosis. Liver alterations following by-pass are usually reversible and respond to the infusion of medicaments. The indication for surgical re-establishment of continuity, in which, if timely, leads to normalisation of liver shape and function, must be chosen without hesitation when changes, albeit reversible, appear to threaten life and resist treatment, and in all cases where biopsy points to progression towards irreversible sclerosis.