['Cytomegalovirus (CMV) infection is associated with reduced graft and patient survival among kidney recipients. The highest risk of CMV infection occurs in CMV-naive recipients of kidneys from seropositive donors (D+/R-). Optimal CMV prophylaxis is not established. This prospective cohort study compared the safety and efficacy of prophylaxis with 12 versus 24 weeks of oral ganciclovir.', 'We prospectively administered 24 weeks ganciclovir to 31 D+/R- recipients. The control group comprised 39 patients transplanted in the immediately preceding era who received a 12-week course of prophylaxis. All patients received cytolytic therapy within the first month, as well as a tacrolimus-based maintenance regimen. A logistic regression model was fit to examine the relationship between 24 weeks ganciclovir prophylaxis and the odds of developing CMV infection by one year.', 'Groups were matched, though the 12-week cohort had more delayed graft function than their 24-week counterparts (45% vs. 29%, P=0.04). CMV infection occurred in 31% and 7% patients in the 12-week and 24-week groups, respectively (P<or=0.01). Mean time to development of CMV infection was 17.5+/-2.2 weeks in the 12-week, and 22.0+/-10.0 weeks in the 24-week, groups (P=0.79). Both 24 weeks ganciclovir prophylaxis (O.R. 0.15, 95% C.I. 0.03-0.91, P=0.04) and delayed graft function (O.R. 4.49, 95% C.I. 1.67-36.56, P<0.01) were associated with CMV infection.'] Is 24-week oral ganciclovir prophylaxis in kidney recipients associated with reduced symptomatic cytomegalovirus disease compared to a 12-week course?