Upper respiratory illnesses, including colds and influenza-like illnesses, are common among college and university students. We have established an ongoing, serial cohort study to assess the occurrences of these illnesses among college and university students as well as the impact of these illnesses on overall health, school and work performance, and health care use. In this paper we report on the first 2 years of this study (2002-2003 and 2003-2004). For each year, more than 4000 students responded to the e-mail invitations to participate, and they provided more than 3000 person-seasons of follow-up information during the monthly surveys conducted November-April. In both years, colds and influenza-like illnesses were common and associated with significant numbers of bed days, reduced activity days, school and work loss, impaired school performance, and increased health care utilization. Efforts to prevent upper respiratory illnesses among college and university students could improve their health and reduce health care utilization during the winter months.