Focal nodular hyperplasia (FNH) is a benign lesion of the liver and is most commonly seen in women in the reproductive age. This article is a retrospective study of FNH.Patients with histologically verified FNH were included. The relationship between tumor size, sex and estrogen was investigated.24 patients were included. In 19 cases, the diagnosis was made coincidentally during the investigation or treatment of another disease. There was no difference in average tumor-size between sexes, but estrogen-treated women had larger tumors. Biopsies were needed in order to establish the diagnosis and to rule out malignancy. In most cases, the chosen strategy of management was expectancy rather than surgery.FNH is a benign liver disease and is often diagnosed coincidentally. An association between tumor size and estrogen treatment remains elusive. Diagnostic Imaging with contrast enhancement may produce characteristic features of FNH. However, biopsy remains the best option to diagnose FNH and to rule out malignancy.