Renal biopsy is a technically difficult procedure in children. Some centers are still using general anesthesia, fluoroscopy, and/or open renal biopsies in young infants. We evaluated the safety and efficacy of two different types of 18-gauge, automated, spring-loaded disposable biopsy needles in 43 children, aged 8 months to 16 years, under ultrasound guidance. Microinvasive ASAP18 (Boston Scientific Corp, Watertown, MA) needles retrieve 19-mm long specimens only, while Ultra-Cut needles (Medical Device Technologies, Inc, Gainesville, FL) are adjustable and can retrieve 6-, 13-, or 19-mm specimens. Technically, Ultra-Cut needles are easier to use in infants or when small kidneys are biopsied. While two infants required intravenous ketamine, the remaining biopsies were done with intravenous sedation. Ultrasound-guided renal biopsy with 18-gauge microinvasive needles and intravenous sedation is a safe and reliable method for obtaining biopsy specimens in older children, as well as in small infants.