The just deserts model rests on retributive principles but assumes proportionality in assigning punishments. The resulting sentencing models that have been adopted seek to reduce the judicial discretion involved in strict proportionality and to avoid sentencing disparity. Minnesota, the first State to develop sentencing guidelines based on a just deserts model, modified the model by considering the offender's prior record and by constraining sentence lengths to avoid prison overcrowding in accordance with a legislative mandate that no new prisons be built. All but 1 percent of current sentences are within the resulting guidelines. Pennsylvania's guidelines, developed independently of prison capacity considerations, rest on two factors: offense seriousness and prior record. The system appears to be succeeding in reducing both sentencing disparity and undue leniency, but prison overcrowding has not been controlled. These two systems show the potential of sentencing guidelines for controlling prison overcrowding and the need for central coordination. Figures, tables, and 23 references are supplied.