Primary biliary cirrhosis (PBC) is characterized by frequent presence of antimitochondrial antibodies (AMAs). The sensitivity and specificity of AMA for PBC are both greater than 90%-95%, so the presence of AMA in serum is the major hallmark in PBC. However, it has long been recognized that in 5%-10% of patients the clinical, biochemical and histological features are diagnostic for PBC, but their sera are consistently tested negative for AMA/AMA-M2. This study aimed to evaluate whether the presence of AMA alters the clinical, serological and histological features of the disease.Clinical data of 70 patients clinically and/or histologically diagnosed with PBC were reviewed. AMA-negative and AMA-positive patients were compared in terms of clinical, biochemical, immunological and histological features.At presentation, 11 patients were serum AMA/AMA-M2 negative. At the initial visit, AMA-negative and AMA-positive patients were similar in terms of age, sex, clinical manifestations, liver biochemistries and histological findings. The mean level of serum immunoglobulin M (IgM) was significantly lower in AMA-negative PBC patients than in AMA-positive PBC patients (2851+/-1418 mg/L vs 6361+/-4928 mg/L, P=0.033). Serum antinuclear antibodies (ANA) and/or smooth muscle antibodies (SMA) were more frequently positive in the AMA-negative PBC patients than in the AMA-positive patients (81.8% vs 40.7%, P=0.031).AMA-negative PBC patients are characterized by relatively lower levels of serum IgM and a higher prevalence of serum ANA/SMA and are not associated with substantial differences in the clinical biochemical and histological spectrum of the disease.