Anecdotal evidence has associated the artificial sweetener aspartame with a number of symptoms of central nervous system (CNS) dysfunction. There are, however, little scientific data concerning the effect of aspartame upon complex mental operations such as those necessary for flying an aircraft. Thirteen pilots were tested in a double-blind study using the SPARTANS cognitive test battery of aviation-relevant information-processing tasks. These tasks relate to perceptual-motor abilities, spatial abilities, working memory, attentional performance, risk taking, processing flexibility, planning and sequencing ability. Subjects were tested over five sessions consisting of pretest and posttest controls and three randomly ordered treatment sessions. The treatment conditions involved an aspartame dose of 50 mg/kg body weight, a placebo condition, and an ethyl alcohol (0.1% BAL) condition as the positive control. No detectable performance decrements were associated with the aspartame condition, although decrements in psychomotor and spatial abilities were detected in the ethanol condition. Results were found to be consistent with prior flight-simulator studies of alcohol, but do not appear to support the concerns expressed in anecdotal testimony regarding the deleterious effects of aspartame upon cognitive performance.