Toxic oil syndrome (TOS) resulted from consumption of rapeseed oil denatured with 2% aniline and affected more than 20,000 persons. Eighteen years after the epidemic, many patients continue to report neurologic symptoms that are difficult to evaluate using conventional techniques. We conducted an epidemiologic study to determine whether an exposure to toxic oil 18 years ago was associated with current adverse neurobehavioral effects. We studied a case group of 80 adults exposed to toxic oil 18 years ago and a referent group of 79 adult age-and sex-frequency-matched unexposed subjects. We interviewed subjects for demographics, health status, exposures to neurotoxicants, and responses to the Kaufman Brief Intelligence Test (K-BIT), Programa Integrado de Exploracion Neuropsicologica (PIEN), and Goldberg depression questionnaires and administered quantitative neurobehavioral and neurophysiologic tests by computer or trained nurses. The groups did not differ with respect to educational background or other critical variables. We examined associations between case and referent groups and the neurobehavioral and neurophysiologic outcomes of interest. Decreased distal strength of the dominant and nondominant hands and increased vibrotactile thresholds of the fingers and toes were significantly associated with exposure to toxic oil. Finger tapping, simple reaction time latency, sequence B latency, symbol digit latency, and auditory digit span were also significantly associated with exposure. Case subjects also had statistically significantly more neuropsychologic symptoms compared with referents. Using quantitative neurologic tests, we found significant adverse central and peripheral neurologic effects in a group of TOS patients 18 years after exposure to toxic oil when compared with a nonexposed referent group. These effects were not documented by standard clinical examination and were found more frequently in women. Environmental Medicine Article fictitious or exaggerated. As a result, some TOS patients may have been incorrectly classified as "chronic complainers," when instead they suffer from a genuine neurologic disorder.A study that used the Nottingham Selfperceived Health Profile to evaluate a subcohort of TOS patients found that, as a group, TOS patients felt that they were in very poor health and that they suffered from a number of health problems (Gomez et al. 1998).Although neurologic findings may be difficult to quantify, within the last few years techniques have been developed to measure neurologic abnormalities more accurately (Gerr et al. 1990(Gerr et al. , 1991Letz 1991). Quantitative neurologic testing has been successfully used to characterize other diseases with subtle neurologic findings, such as the epidemic of optic and peripheral neuropathy that occurred in Cuba (Cuba Neuropathy Field Investigation Team 1995); EMS, a disease clinically similar to TOS (Philen and Posada 1993;Sullivan et al. 1996); and other diseases related to toxic environmental exposures (Stokes et al. 1998).The hypothesis of this ...