Efforts to structure sentencing through guidelines involve a fundamental dilemma for the sociology of law; guidelines attempt to emphasize formal rationality and uniformity while allowing discretion to tailor sentences to fit situations and characteristics of individual defendants when courts deem it warranted (substantive rationality). This exercise of substantive rationality in sentencing based on extralegal criteria deemed relevant by local courts risks the kind of unwarranted disparity that guidelines were intended to reduce. The authors use statistical and qualitative data from Pennsylvania, where state courts have operated under sentencing guidelines for over a decade. They analyze extralegal differences in three county courts' sentencing outcomes, and document ways in which substantive rational sentencing criteria are intertwined with defendants' exercise of their right to trial and their race and gender. Footnotes, tables, references, appendix