Perinatal units differ in their ability to prevent patient injury and medical malpractice litigation. Obstetrical units with favorable performance are distinguished by common organizational and clinical features. Organizationally, they resemble what behavioral scientists define as "high-reliability organizations" (i.e., the ability to operate technologically complex systems essentially without error over long periods). Clinically, practices are based on nationally recognized guidelines and/or an operational philosophy of "safety first." These organizational and clinical features are described so that physicians, nurses, and administrators might view their own clinical environments in the context of this perspective.