Objectives: Low-dose valganciclovir prophylaxis is still under investigation in renal transplant procedures. Our aim was to assess the cost effectiveness of 450 mg versus 900 mg valganciclovir prophylaxis in kidney transplant recipients. Materials and Methods: In this prospective trial, 201 kidney transplant patients were randomized (1:1) to receive 450 mg/d (group 1, n = 100) or 900 mg/d (group 2, n = 101) valganciclovir prophylaxis for the first 6 months after transplant. Patients were studied for incidence of cytomegalovirus disease, leukopenia episodes, rejection episodes, and graft outcomes along with associated costs over 1 year. Costs (in US dollars) of treatment of rejection were also analyzed. Results: Demographic features of the studied groups were comparable. We found that the cost of cytomegalovirus care in group 1 patients was significantly lower (by 50% at 6 months; P < .001), with less leukopenia episodes (P = .04), lower doses of granulocyte colony-stimulating factor (by 30% at 6 months; P = .03), higher doses of mycophenolate mofetil (P = .04), and less rejection episodes (P = .01) compared with group 2. In group 2, there were more episodes of cytomegalovirus infection (P = .052) and BK virus nephropathy (P = .04). Graft and patient outcomes were satisfactory in both groups. Conclusions: Low-dose valganciclovir for cytomegalovirus prophylaxis after renal transplant is safer, effective and without breakthrough infection, and less costly than using the usual dose.