BACKGROUND: Liver disease is a major cause of morbidity and mortality worldwide. Large numbers of liver function tests (LFTs) are performed in primary care, with abnormal liver biochemistry a common finding. Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver injury. Metabolic syndrome, common in people from South Asia, is an important risk factor for NAFLD. AIM: It is hypothesised that a large gap exists between numbers of patients with abnormal LFTs and those with recorded liver diagnoses, and that NAFLD is more common among adults of South Asian ethnic groups. DESIGN AND SETTING: A cross-sectional study of 690,683 adults in coterminous general practices in a region with high ethnic diversity. METHOD: Data were extracted on LFTs, liver disease, and process of care measures from computerised primary care medical records. RESULTS: LFTs were performed on 218,032 patients, of whom 31 627 had elevated serum transaminases. The prevalence of abnormal LFTs was highest among individuals of Bangladeshi ethnicity. Of the patients with abnormal LFTs, 88.4% did not have a coded liver diagnosis. NAFLD was the most frequently recorded liver disease and was most common among Bangladeshi patients. In a multivariate analysis, independent risk factors for NAFLD included Bangladeshi ethnicity, diabetes, raised BMI, hypertension, and hypercholesterolaemia. CONCLUSION: Abnormal LFTs are common in the population, but are underinvestigated and often remain undiagnosed. Bangladeshi ethnicity is an important independent risk factor for NAFLD.