Because persons with disabilities (PWDs) use health and social services extensively, both the United States and the United Kingdom have begun to integrate care across systems. Initiatives in these two countries are examined within the context of the reality that personal needs and use of systems differ by age and by type and severity of disability. The lessons derived from this scrutiny are presented in the form of five "laws" of integration. These laws identify three levels of integration, point to alternative roles for physicians, outline resource requirements, highlight friction from differing medical and social paradigms, and urge policy makers and administrators to consider carefully who would be most appropriately selected to design, oversee, and administer integration initiatives. Both users and caregivers must be involved in planning to ensure that all three levels of integration are attended to and that the borders between medical and other systems are clarified.