The multiple-view focused assessment with sonography for trauma (FAST) exam is an integral tool in the assessment of blunt abdominal trauma. A prospective observational study was performed to compute the average minimum volume of detectable intraperitoneal fluid with the pelvic views of the FAST exam. All adult patients from October 1999 to May 2001, who presented to the ED with blunt abdominal trauma and underwent a clinically indicated diagnostic peritoneal lavage (DPL), were candidates for admission to the pelvic ultrasound study. In the supine position, patients were administered lavage fluid in 100 cc increments until the examiner detected the fluid on ultrasound. An independent reviewer also examined the hard-copy ultrasound images for fluid detection. Patients were excluded if they had (1) a positive DPL for hemoperitoneum (defined as 10 cc of gross blood or >100,000 red blood cells/mL), (2) a positive initial ultrasound for free fluid, or (3) lacked sufficient hard-copy ultrasound images. The mean minimal volume of fluid needed for pelvic ultrasound detection by the examiner and reviewer was 157 and 129 cc (n = 7), respectively. The median quantity of fluid for ultrasound detection by both the examiner and reviewer was 100 cc. The pelvic views of the FAST exam identified a significantly smaller quantity of intraperitoneal fluid than previous studies of the right upper quadrant single-view exam.