The results of the study suggest that although downward departures for substantial assistance might be an important source of unwarranted disparity in the Federal sentencing process, the disparity for the most part does not result from idiosyncratic decisions made by individual prosecuting attorneys. The findings also indicated that significant interprosecutor variation remained after taking into account offender characteristics, case characteristics, and the district in which the case was adjudicated. Future research is recommended to continue to examine the factors that influence whether an offender would receive a downward departure for providing substantial assistance and to explore whether individual prosecutors use a similar decision calculus in making these decisions. An important and highly discretionary component of the Federal sentencing guidelines is the downward departure for providing substantial assistance. It was argued that the substantial assistance departure might produce the type of unwarranted sentencing disparity that the guidelines were intended to eliminate. Using data on offenders sentenced in three U.S. district courts and a multilevel modeling strategy, this study investigated whether interprosecutor disparity existed in the likelihood of substantial assistance departures and in the criteria that prosecutors used in deciding whether to file a motion for a substantial assistance departure. Tables, references, and appendixes