This paper reviews more than 30 studies of health care utilization in which the effects of religion variables are examined, an area previously unreviewed. The authors found that over three-quarters of these studies reported significant religious differences in rates of utilization. The most common operationalization of religion was religious affiliation (typically Protestant vs Catholic vs Jewish), although the effects of religious attendance and religiosity were occasionally examined. Most major areas of health care use are represented in this literature, including psychiatric care, maternal and child health services, dental care, and physician and hospital utilization. Despite the preponderance of significant findings, it is difficult to isolate any consistent trends, although low-order analyses seem to suggest that Jews are higher utilizers than non-Jews. New findings presented from a study in Appalachia were inconclusive. The authors discuss the conceptual limitations inherent in ways in which health services researchers typically investigate the effects of religion. Drawing on recent work in the epidemiology of religion, several recommendations are offered regarding the prospect of future research in this area.