The economic growth and development of 12 rural primary care practices established by the National Health Service Corps (NHSC) in the Pacific Northwest between 1973 and 1975 was examined. The 12 practices represented four types of rural health care delivery systems based on the size of the service area, the presence and type of hospital within that service area, and the number and kinds of providers in the service area. The results indicate that rural primary care practices, in at least one region of the United States, can approach financial self-sufficiency in two to three years. However, practices grow at different rates, depending on the nature of their surrounding environment. Provider retention appeared to be correlated with practice growth and stability. In the setting studied practices in which physicians were the major providers and had ready access to hospital facilities grew relatively rapidly, approaching financial self-sufficiency within two to two-and- a-half years. Practices which contained physicians who did not have ready access to a hospital grew slower and had more erratic growth patterns than other types of practices. Practices staffed solely by nurse practitioners, initially had slow growth, but began to approach self-sufficiency after three years of operation. The study has improved the ability of the Public Health Service, HEW, Region X to predict the rate of growth of different types of rural primary care practice. This has proven helpful in allowing the Public Health Service to more accurately advise inquiring rural communities about alternatives for health care delivery systems.