Eighty-four consecutive subjects with nonalcoholic fatty liver disease (NAFLD) were tested for non-organ-specific autoantibodies (NOSA) by indirect immunoflorescence. Indices of insulin resistance and biochemical and anthropometric parameters were assessed. The overall prevalence of anti-nuclear-antibodies (ANA), smooth muscle antibodies (SMA) and anti-mitochondrial-antibodies (AMA) was 35.7% (30/84), 18 subjects (21.4%) being positive for ANA, 4 (4.7%) for SMA, 6 for ANA and SMA, and 2 for AMA. NOSA-positive subjects were older (P < 0.01) and mostly females (63.3%). No significant difference was found in the age-corrected parameters studied, except for copper and ceruloplasmin, which was more elevated in NOSA-positive patients. The subset of high titer (&GE;1:100) ANA-positive patients had significantly (P < 0.05) greater insulin resistance than ANA-negative patients. In contrast, SMA-positive patients had higher gammaglobulin and significantly lower insulin resistance as compared to high-titer ANA-positive patients. In 3 NOSA-positive but not in NOSA-negative patients, liver biopsy disclosed features of overlapping NASH with autoimmune hepatitis, partially responding to diet combined with steroid treatment. In conclusion, NOSA positivity in NAFLD is more prevalent than in the general population. High-titre ANA but not SMA positivity is associated with insulin resistance.