"Zero-hour" renal allograft biopsy provides valuable diagnostic information for comparison to subsequent kidney material. However, the invasive nature of the biopsy procedure tends to limit its widespread use in many centers. We undertook this retrospective study to examine the rate and clinical importance of complications in our series of patients routinely undergoing zero-hour biopsies performed between 1994 and 2001. Two hundred thirty-six zero-hour biopsies included only one sample performed with a 14G needle from lower posterior part of kidney by using a manual tru-cut technique. Doppler ultrasonography was performed after first 5 days. An average of 34 +/- 19 glomeruli were obtained in the biopsies. The biopsy specimens were adequate for diagnosis in 77% of the procedures. Ten (4%) patients experienced complications of intraparenchymal arteriovenous fistula (n = 4), which regressed spontaneously; perirenal hematoma (n = 4); intraparenchymal hematoma (n = 2); and a minimal perirenal collection (n = 41). We conclude that zero-hour biopsy is a safe diagnostic method. The rate of complications is low, as well as generally mild and self-limiting.