The UFOMOD program system is an advanced probabilistic accident consequence assessment (ACA) code. Its structure and modeling are based on the experience gained from applications of the old UFOMOD code during and after the German Risk Study Phase A, the results of scientific investigations performed within Phase B, the ongoing Commission of the European Communities Methods for Assessing the Radiological Impact of Accidents project, and the requirements resulting from the extended use of ACA codes to help in decision making. The structure of the program system and essential characteristics of important submodules are described. Selected results of recent investigations illustrate the flexibility and broad applicability of the new UFOMOD code.