We evaluated the clinical course of 700 renal transplantations, including 1,305 transplant histologies performed in 611 patients between 1970 and 1988, to estimate the influence of cyclosporine A (CsA) after kidney transplantation on the incidence of recurrent or de novo renal disease. Primary renal disease recurred in 11 of 583 functioning transplants (1.9%) with transplant loss in seven patients (1.2%): focal segmental glomerulosclerosis (FSGS, three patients); membranous glomerulonephritis (GN, one patient); mesangiocapillary GN (one patient); rapidly progressive IgA nephropathy (one patient); hemolytic-uremic syndrome (HUS, three patients); and oxalosis in two transplants (one patient). De novo renal disease occurred in six patients (1.0%), including mesangiocapillary GN type I (three patients); nonpurulent focal GN in septicemia (one patient); HUS (one patient); and nodular glomerulosclerosis in steroid diabetes (one patient). De novo membranous GN was seen in 14 additional cases (2.4%). No statistically significant difference could be established between the treatment groups without (n = 225) and with (n = 358) CsA in recurrent and de novo renal disease (n = 7/225 v 10/358, NS); in recurrent and de novo GN (n = 4/225 v 6/358, NS); in recurrent FSGS (n = 1/7 v 2/8, NS); in recurrent and de novo HUS (n - 1/1 v 2/7, NS); and in de novo membranous GN (n = 7/225 v 7/358, NS). Transplant loss by recurrent and de novo GN was higher without than with CsA (n = 4/4 v 1/6, P = 0.004). On the basis of our investigation, we conclude that recurrent and de novo renal disease in the transplant occur rarely and are not prevented by CsA. However, even if the incidence of transplant GN is unchanged by CsA treatment, its clinical course seems to be mitigated. CsA treatment also does not increase the incidence of HUS.