OBJECTIVE In a randomized control trial of mycophenolate mofetil (MMF) versus azathioprine (AZA) with cyclosporine and steroids, we demonstrated that MMF reduced acute rejection (AR) among renal allograft recipients (RTX) who were of low to moderate risk. However, 10% had AR when converted from MMF to AZA at 6 months, postrenal transplantation (RT). Two clinical markers, abnormal serum creatinine (SCr) and proteinuria at 6 months, post-RT, were associated with AR postconversion. The present study examined the safety of such conversion in selected high-risk RTX at 1 year of MMF therapy. METHODS Thirteen high-risk RTX receiving MMF for either high panel reactive antibody (n = 9) or following AR (n = 4), with normal SCr and no proteinuria at 1 year, were selected for conversion. The incidence of AR, adverse events, and renal parameters (SCr, creatinine clearance, proteinuria) at 6 months postconversion was evaluated. Eight high-risk RTX who did not meet these selection criteria were retrospectively reviewed and used as controls. RESULTS Renal parameters (SCr 123 +/- 26 vs 129 +/- 27 mumol/L; pre- vs postconversion) were not significantly different; no episodes of AR or proteinuria were documented. Azathioprine was discontinued in two patients due to leukopenia. In the control group, one patient had graft loss from chronic rejection, whereas one developed posttransplant lymphoproliferative disease necessitating MMF withdrawal. CONCLUSIONS These results suggest that selective conversion from MMF to AZA after 1 year is safe, even in high-risk RTX. Normal SCr and absence of proteinuria are good screening parameters to identify patients at low risk for AR following such conversion.