Numerous studies with <20 years of follow-up have shown no significant long-term consequences of living kidney donation. However, hypertension and proteinuria have both been described; it is unknown whether either complication presages future kidney dysfunction. Between June 1, 1963, and December 31, 1979, we did 773 living donor kidney transplants for 715 recipients. We attempted to contact all donors to determine long-term outcome regarding their remaining kidney. We obtained information on 464 (60%) of the donors. Of these, 84 had died and 380 were alive; of the 380, 256 returned a questionnaire and 125 sent in current laboratory results and/or records of a recent history and physical examination. Of the 84 donors who had died, three were known to have had kidney failure. Of the 380 still alive, three had abnormal kidney function and two had undergone transplantation. The remaining donors had normal kidney function. The rate of proteinuria and hypertension was similar to the age-matched general population. We conclude that most kidney donors have normal renal function 20-37 years post donation. However, some do develop renal dysfunction; some, renal failure. Our data underscore the need to develop prospective trials for long-term follow-up of kidney donors.