Membranous nephropathy is a common cause of nephrotic syndrome in adults. Although some patients with membranous nephropathy achieve a spontaneous remission, renal function continues to deteriorate in others. We conducted a prospective randomized trial evaluating monotherapy with tacrolimus to achieve complete or partial remission in patients with biopsy-proven membranous nephropathy. Twenty-five patients received tacrolimus (0.05 mg/kg/day) over 12 months with a 6-month taper, whereas 23 patients were in the control group. The probability of remission in the treatment group was 58, 82, and 94% after 6, 12, and 18 months but only 10, 24, and 35%, respectively in the control group. The decrease in proteinuria was significantly greater in the treatment group. Notably, six patients in the control group and only one in the treatment group reached the secondary end point of a 50% increase in their serum creatinine. No patient in the tacrolimus group showed a relapse during the taper period. Nephrotic syndrome reappeared in almost half of the patients who were in remission by the 18th month after tacrolimus withdrawal. We conclude that tacrolimus is a very useful therapeutic option for patients with membranous nephropathy and preserved renal function. The majority of patients experienced remission with a significant reduction in the risk for deteriorating renal function.