Over a period of 37 years we performed renal biopsies 1812 times in 1638 subjects. Tissue adequate for interpretation was obtained in 1593 subjects (88%). Complications occurred in 7% of the total biopsies performed, consisting of gross hematuria lasting for more than 12 hours (3%), pain lasting for more than 12 hours (4%), a palpable hematoma (1%), infection (0.2%), and death (0.2%). Complications were higher when the biopsy yielded unsatisfactory samples (9.5%), although there were no deaths. Complications were not related to age but an elevated BUN appeared to be associated with a higher rate of complications, although this was not statistically significant. Deaths appeared to occur at unpredictable intervals and in retrospect could not have been foreseen.