Purine analogues are major drugs in the treatment of inflammatory bowel diseases (IBD). We present four cases of nodular regenerative hyperplasia of the liver (NRH) developed in patients with IBD treated with azathioprine. All patients had either abnormal liver tests and/or low platelet count. Although biochemical and hematological abnormalities regressed after azathioprine withdrawal, the long term evolution of the hepatic lesions (and the risk to develop further complications including portal hypertension) remains to be determined. Male gender seems to be a major risk factor by providing a predisposing pharmacogenetic profile of purine analogue metabolism. Clinicians should be aware of this serious complication which may occur with any of the purine analogues (azathioprine, 6-mercaptopurine, and 6-thioguanine).