In the United States various forms of managed care have been introduced to control the use of expensive medical services. One of the most prominent involves utilization review of hospital admissions. While reviewing the appropriateness of inpatient treatment is appealing in principle, its application is made difficult by clinical uncertainty. Managed care plans develop and implement review criteria often without the guidance of clear clinical norms of treatment. Under these conditions, we suggest that utilization review organizations (UROs) can be expected to develop “styles” of review that respond to clinical uncertainty, influenced by their experience, professional orientation, and financial incentives. Two review styles are explored in this paper: standardization, where the URO reduces the variance in clinical practices by eliminating those practices that deviate from professional norms and stringency, whereby the URO shifts the distribution of clinical practice as it tries to change the professional norms of practice. Data from a 1992–1993 national survey of utilization review organizations are used to test whether UROs have review styles that systematically respond to organizational attributes, economic pressures, and clinical uncertainty associated with three medical conditions: cardiac catheterization, low back pain, and adolescent depression. UROs were found to adopt more stringent review strategies for conditions with weaker norms of appropriate treatment. Financial incentives and organizational experience are positively related to greater stringency. Standardization responds to professional orientation and organizational experience. Variation in the review styles of UROs has implications for the resulting distribution of clinical practices as well as the equity of access to medical care.