Azathioprine (AZA) or 6-mercaptopurine (6-MP) are the immunosuppressive drugs of choice in the treatment of inflammatory bowel disorders (IBD). Optimal dosage for AZA is around 2.5 mg/kg body weight and induction of remission by these drugs may take 6 - 7 months. Intramuscularly applied Methotrexate (MTX) is the second choice, while its efficacy starts earlier than that of AZA; studies assessing oral low-dose MTX treatment are lacking. Cyclosporin is the standard treatment in case of steroid-refractory severe ulcerative colitis. This drug may also be used in patients with severe extraintestinal manifestations of IBD. Regarding other immunosuppressive drugs such as mycophenolic acid or 6-thioguanine respective controlled clinical study data are not available. The risk of malignancy using immunosuppressive drugs such as AZA is low and furthermore, especially AZA and 6-MP can be used rather safely during pregnancy.