In the past 10 years we have examined 20 children with inflammatory liver disease associated with high serum titers of anti-liver-kidney microsome antibody (anti-LKM). The first hepatic symptoms were progressive fatigue and jaundice, the fortuitous finding of hepatomegaly or splenomegaly with raised transaminase activity, or an acute hepatitis-like illness. At the time of diagnosis, hepatomegaly was present in 18 children, splenomegaly in 16, jaundice in nine, and ascites in two. Serum alanine transferase activities were elevated in all but two, who had already received steroids. Serum total gammaglobulin values were greater than 2.0 gm/dl in 16 children, prothrombin activity less than or equal to 60% in six, and serum titer of anti-LKM between 1:100 and 1:100,000. All children but one had cirrhosis, and histologic signs of aggressivity were present in 14. In 11 children one or more extrahepatic diseases were present, including type 1 diabetes, vitiligo, glomerulonephritis, autoimmune hemolytic anemia, hypoglycemia with hyperinsulinism, autoimmune thyroiditis, chronic mucocutaneous candidiasis with hypoparathyroidism, and multiple cutaneous and visceral telangiectasias. Treatment with prednisone and azathioprine improved the liver condition in 16 of the 18 patients given treatment. In eight of them discontinuation of treatment resulted in rapid relapse; 14 are still receiving treatment and have stable hepatic function with follow-up from 8 months to 6 1/2 years. Only two are free of treatment. Four children died, two in spite of immunosuppressive therapy, one during a relapse, and one of extrahepatic disease. These results indicate that this autoimmune inflammatory liver disease may have onset early in life, with several clinical patterns; is frequently associated with certain types of extrahepatic manifestations of autoimmune origin; and is a potentially fatal disease for which immunosuppressive treatment must be started early.