The purpose of this systematic review was to examine the evidence for the use of the Iowa Oral Performance Instrument (IOPI) to measure strength and endurance of the tongue and hand in healthy populations and those with medical conditions. A systematic search of the scientific literature published since 1991 yielded 38 studies that addressed this purpose. The IOPI was used primarily for tongue strength (38 studies) and endurance (15 studies) measurement; relatively few studies measured hand strength (9 studies) or endurance (6 studies). The majority of the studies identified used the IOPI as an evaluation tool, although four used it as an intervention tool. Half the studies were conducted in healthy people, primarily adults. Most of the other participants had disorders with dysphagia, primarily Parkinson's disease or head or neck cancer. Age and gender, as well as a number of medical conditions, influence the values of tongue and hand strength. There is sufficient evidence to support the use of the IOPI as a suitable tool for measuring tongue strength and endurance and as an assessment tool for intervention studies, and there is growing support for its use to assess hand strength and endurance in healthy and clinical populations.