The objective of this article is to determine if health care reform in Massachusetts in 2006 was associated with a change in ED utilization by the uninsured for asthma and upper respiratory tract infection (URI). We performed a retrospective pre-post study in an urban tertiary-care teaching hospital. Subjects included all patients, ages 2-54, who presented to the ED with asthma or URI from January 1 to July 31 for each of the 3 years before health care reform and for the period after the insurance mandate officially went into effect on January 1, 2008. We used chi-square analysis to compare the frequency of utilization of the ED by uninsured patients before and after the implementation of an individual health insurance mandate in Massachusetts. For the period before the implementation of health reform, an annual average of 301 ED visits for patients with either URI (average n = 131) or asthma (average n = 170) were identified. After health care reform, there were 366 visits found for URI (n = 132) and asthma (n = 234) over a similar time period. There was a statistically significant decrease in ED utilization by the uninsured for URI but not for asthma. As a secondary analysis, visits for patients covered by the uncompensated care pool (UCP) before health care reform was not different from the combined frequency of visits by the remaining uninsured covered by a health safety net pool and those who qualified for the state subsidized Commonwealth Care program after health care reform. In this study, health care reform was associated with a decrease in the number of uninsured patients who presented to the ED with URI but not asthma. This study is limited by its analysis of a single large institution and a limited set of diagnoses.