Metformin is an oral hypoglycemic agent that is commonly used in the treatment of type 2 diabetes mellitus. Although metformin-associated gastrointestinal upset and metabolic acidosis is widely recognized side effect of this drug, metformin-induced liver injury has been rarely reported in the literature. In most cases reported, metformin-induced liver injury was associated with concomitant intake of other hepatotoxic drugs. Here, we report a case of a 70-year-old white woman who suffered metformin-induced liver injury 5 weeks after starting on this medication, and she was not on any other hepatotoxic agent. With increasing prescription of metformin, this case deserves particular attention for this rare but important side effect.