The alarming increase in hospital emergency room (ER) usage, especially by inner city populations, is an important indicator of the current health care crisis. If neighborhood health centers (HC) are effective in reaching their target population, they should have sufficient impact to stop or reverse this trend. This study tried to measure the impact of the dental HC services on ER usage for dental emergencies. The ER logs of the main hospitals were studied covering a four-year period. The patient's address was coded by census tract to compare ER usage from various areas, especially the HC target area and a second poverty district as comparison area. Dental ER usage from all areas continued to grow with the largest increase occurring from 1969 to 1970. Revised hypotheses were tested in two follow-up studies, one using personal interviews of ER patients and the other using Medicaid payment files. A change in Medicaid payment regulations (20% fee cut) in 1969 had led many dentists to withdraw from the program, but some in the second poverty district had responded by expanding their services to the poor. The HC had an impact, but this was clouded by other powerful changes in the dental health care system for the poor.