AbbreviationsCT, computed tomography; IOUS, intraoperative ultrasonography; LUS, laparoscopic ultrasonography; MRI, magnetic resonance imaging t is a privilege to contribute an article on intraoperative ultrasonography (IOUS) to the series of articles on the history of ultrasound in commemoration of the 50-year anniversary of the American Institute of Ultrasound in Medicine in 2005. On approaching my own 30th anniversary in the practice of diagnostic radiology, it is amazing to reflect back on the uses of A-mode, B-scanning on nonpersistent green fluorescent oscilloscopes, and bistable B-mode scanning as the first primitive diagnostic ultrasonographic tools. Although IOUS began developing in earnest in the late 1970s and early 1980s, after the development of gray scale B-mode ultrasonography and especially after the development of real-time imaging, early investigators were using the more primitive tools as early as the 1960s.One of the very first reports of IOUS was by Schlegel et al 1 in 1961, who used A-mode ultrasonography for the localization of renal calculi ( Figure 1). A-mode was also reported as useful in detection of stones in the gallbladder and common duct in an article by Knight and Newell 2 in 1963 and in another article by Eiseman et al 3 in 1965. A-mode echoencephalography was also reported as useful in delineation of intracerebral mass lesions in a study by Dyck et al 4 in 1966. The inability to display tissue texture in A-mode or bi-stable B-scanning as well as the rather large, bulky size of the equipment limited the more widespread use of IOUS. A small direct-contact ophthalmic B-scanner was developed and proved useful for B-scan ultrasonography during orbital surgery for tumors, as reported by Purnell et al 5 in 1973 (Figure 2), but very little further development was reported until the advent of real-time scanners and smaller, more portable equipment. One of the first reports of real-time B-mode ultrasonographic scanning was by Sigel et al 6 in 1982, which described the use of ultrasonography for precise localization of renal calculi, thereby allowing for the use of smaller nephrotomy incisions, reduced operating room time, and determination that all stone fragments were removed before completion of the procedure. My own experience with IOUS began rather inadvertently in 1983, when I received a call from a distraught surgeon in the operating room, who could not find the intrahepatic abscess that we had shown on preoperative ultrasonography and computed tomography (CT) in a patient