Nephrotic syndrome (NS) is an extremely rare complication of myeloablative allogeneic haematopoietic cell transplantation (HCT) that usually occurs in association with chronic graft-versus-host disease (C-GVHD). We observed an unexpectedly high incidence of NS in a cohort of 163 consecutive patients undergoing non-myeloablative HCT from a related human leucocyte antigen-compatible donor. Seven patients developed NS at a median 318 d post-transplant (range 119-1203 d; cumulative incidence 6.1%). The median age at onset of NS was 46 years (range 33-59 years); three of the seven patients had no evidence of C-GVHD while four had accompanying limited C-GVHD. At diagnosis, median proteinuria was 16.5 g/24 h (range 3-24 g/24 h). Renal biopsy was performed in four cases and revealed membranous nephropathy. NS was not always associated with other symptoms of C-GVHD, and in contrast to previous reports, usually did not improve with the re-initiation of aggressive immunosuppression, resulting in progressive renal failure necessitating dialysis in three of seven cases. Membranous nephropathy resulting in NS is a previously unrecognised and clinically significant complication of non-myeloablative HCT.