BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease involving the motor neuron of the cerebrum, brain stem, and spinal cord. It has been suggested that various occupational or environmental agents could be a cause of ALS. We report upon a case of a person contracting ALS who experienced a long-time exposure to pesticides, implying that pesticides are probable causal agents of ALS. CASE REPORTS: The patient has been experiencing shoulder pain and limitation of movement that started abruptly about three years ago. Over time, these symptoms have become aggravated despite ongoing therapies including medication. After two years, he was diagnosed with ALS through electromyography, nerve conduction velocity and many laboratory tests at a university hospital in Seoul. His social and medical history was non-specific. The patient had worked for about 15 years at a waste disposal site and mainly destroyed glass bottles containing pesticides. During this period, his respiratory tract and skin were exposed to various raw pesticides without appropriate personal protective equipment. He did this job one or two times a week and worked for two or more hours without a break. Through an investigation into the patient's working environment, significant levels of dichlorvos, one of the organophosphates, were detected. CONCLUSIONS: The study results revealed that the patient was exposed to considerable doses of pesticides as opposed to men spraying pesticides. Although controversial, pesticide exposures have been associated with ALS. However, we suggest that in this case the possibility that these pesticide exposures acted as a causal agent for the diagnosed ALS based on plausible biological mechanisms and epidemiologic data.