We report the case of a 66-year-old male with ulcerative colitis diagnosed in 1987, who had been treated with azathioprine (AZA) for the past two years (average dose about 1.6 mg/kg/day), In May 1999 he presented with painless jaundice, fatigue and recent weight loss. Cholestatic enzymes were elevated, alpha -fetoprotein was normal and hepatitis B/C serology negative. After diagnosis of veno-occlusive disease (VOD) and hepatocellular carcinoma (HCC) via biopsy, tumour resection was performed. The histology was typical for a well-differentiated HCC with trabecular and pseudoglandular structures. Neighbouring liver tissue was atrophic, with nodular regenerative hyperplasia (NRH), peliosis-like sinusoidal ectasias and intra-sinusoidal accumulation of blood, associated with peri-sinusoidal fibrosis, Although none of the well-established risk factors for HCC such as cirrhosis, hepatitis B/C, metabolic liver disease or toxins were present, this patient developed HCC. This and previous reports suggest that NRH and/or VOD associated with AZA represent a risk factor for HCC. AZA should therefore not only be stopped in patients with NRH/VOD but patients should also be screened for HCC. Eur J Gastroenterol Hepatol 13:287-290 (C) 2001 Lippincott Williams & Wilkins.