This article presents the case of a 16-year-old girl with posterior reversible leukoencephalopathy syndrome (PRES) after medication with cyclosporine A for Crohn's disease. The PRES consists of lesions on the basis of a vasogenic edema of various etiologies. The initiation of this syndrome can be due to immunosuppressive medication as in this case but many other drugs or different underlying diseases can also result in PRES. The most important therapeutic measures are to stop the causative medication and to start antihypertensive medication and possibly other symptomatic forms of therapy.