Over the last few years spring-driven mechanical biopsy guns have been introduced for performing renal biopsies. There has been little research done comparing these guns with traditional hand-driven needles in performing biopsies of native kidneys. We wished to compare our experience with the two needle types. We studied retrospectively the results and complication rates of 155 native kidney biopsies. Sixty-nine were performed with hand-driven 14-gauge needles and eighty-six with 18-gauge, spring-driven biopsy guns. Sufficient tissue for diagnosis was obtained in 96% of cases in the hand-driven group compared with 99% in the biopsy gun group (P = NS). Complications occurred in six cases in the hand-driven group compared with one case in the biopsy gun group (P = 0.02). As expected, the reported number of glomeruli per core in the 14-gauge cores was greater than in the 18-gauge cores (16.5 v 6.2, P < 0.01). This was partially offset by the greater number of passes made with the smaller needle. We conclude that similar results can be expected from both biopsy methods, with a possible slight decrease in complications using biopsy guns with smaller needle diameters.