As a result of population growth and the development of tube wells, humans' exposure to arsenic has increased over the past few decades. The natural course of organ damage secondary to arsenic exposure is not yet well understood. In Toroku, Japan, an arsenic mine was intermittently operated from 1920 to 1962, and residents were exposed to high concentrations of arsenic. In this paper, we analyzed 190 consecutive residents for whom detailed records of neurological symptoms and findings were obtained from 1974 to 2005. All participants were interviewed regarding the presence of general, skin, hearing, respiratory, and neurological symptoms. Neurological symptoms were classified into extremity numbness or pain, constipation, dyshidrosis, sensory loss, and muscle atrophy. Superficial and vibratory sensation was also evaluated. More than 80% of participants experienced extremity numbness, and numbness was the most common neurological symptom. Numbness was associated with superficial sensory disturbance, and was correlated with the subsequent development of other neurological symptoms, including autonomic and motor symptoms. No previous studies have investigated the natural course of chronic arsenic intoxication; thus, these data serve as a guide for detecting early symptoms due to arsenic exposure.