Prisoner surveys show that under conditions of unpredictability, due in part to the indeterminate sentence, inmates experience higher anxiety levels and lower tolerance for frustration, especially as their parole review dates approach, than they would if they knew their release dates in advance. This anxiety is often accompanied by serious inmate disturbances, and it is felt by inmates' families as well, causing tension in intrafamily relationships. The uncertainty of release date also affects contracts with past or prospective employers. The view that uncertainty causes anxiety is corroborated by the findings of laboratory studies on both humans and animals. In addition to its effects on inmate stress levels, the indeterminate sentence undermines the effectiveness of correctional treatment by its direct linkage with the parole review process, causing many inmates with no genuine interest to enroll and maintain involvement in programs for the sole purpose of obtaining release. Also, more importantly, inmates who may have genuine interest in the programs, may lose it, since, as studies of children, college students and adults (in laboratory, educational, and military contexts) have shown, intrinsic interest and performance is undermined through the delivery of extrinsic rewards. Thus, prisoners may be expected to experience less stress in prison and may be expected to experience less stress in prison and perform more effectively in treatment programs if they have advance knowledge of their release dates. Therefore, ensuring predictability of release will result in benefits for both inmates and the correctional system. The means for accomplishing it are varied and do not necessitate sentencing reforms. Statistical data, notes, and about 40 references are included.