We studied the seroepidemiology of cytomegalovirus (CMV) infection in 59 patients with thermal injuries. Among the 31 patients who were initially CMV seronegative, seven (22.5%) seroconverted. Patients who seroconverted had longer hospital stays (mean, 27 +/- 23.9 days v 14.9 +/- 8.8 days in seronegative patients [P = 0.03]) and they received more blood products (mean, 10.7 +/- 17.9 units v 1.8 +/- 2.8 units [P = 0.02]) than patients who remained seronegative. Among 18 patients who were initially seropositive for CMV, 10 (56%) had a fourfold or greater rise in CMV antibodies, evidence of CMV reactivation. Patients who had reactivated CMV infection tended to be younger, to have a larger burn area, and to have a longer hospital stay. No patient who experienced CMV infection, whether primary or reactivated, had serious complications attributable to CMV.