All states have statutes in place to civilly commit individuals at high risk for violence. The authors address difficulties in assessing such risk but use as an example the task of predicting sexual violence recidivism; the principles espoused here generalize to predicting all violence. As part of the commitment process, mental health professionals, who are often psychologists, evaluate an individual's risk of sexual recidivism. It is common for professionals conducting these risk assessments to use several actuarial risk prediction instruments (i.e., psychological tests). These tests rarely demonstrate close agreement in the risk figures they provide. Serious epistemological and psychometric problems in the multivariate assessment of recidivism risk are pointed out. Sound psychometric, or in some cases heuristic, solutions to these problems are proffered, in the hope of improving clinical practice. The authors focus on how to make these tests' outputs commensurable and discuss various ways to combine them in coherent, justifiable fashions. (Contains 4 tables and 5 footnotes.)