The key histologic feature of nonalcoholic steatohepatitis (NASH) is hepatocellular ballooning (HB). It plays an important role in NASH progression and is an independent predictor of liver mortality. In this review, we identified all studies using metformin in the treatment of nonalcoholic fatty liver disease (NAFLD) that included pre- and post-treatment liver biopsies. We specifically reviewed the effects of metformin on HB. Improved HB was noted in pediatric populations and in those adult patients who were able to lose weight and improve or normalize transaminases during therapy. Previous studies have supported the beneficial effects of metformin in reduction of body weight, improvement of insulin resistance, prevention of complications related to diabetes and chemo-preventive benefits in reducing hepatocellular carcinoma. All these effects make it an attractive treatment consideration for patients with diabetes, and prediabetes who have co-existing NAFLD. Future studies are warranted in order to confirm this effect of metformin on HB and its association with improving long-term outcomes in patients with NAFLD.