Geographic distribution of motor neuron disease and correlation with possible etiologic factors.

Average annual age-adjusted motor neuron disease (MND) mortality rates were mapped for the first time at the county level in the continental United States. Although the great majority of the rates did not differ significantly from the US average, the highest mortality rates were generally found west of the Mississippi and the lowest rates east of the Mississippi. MND mortality was associated with rural farming and socioeconomic status but not with urbanization, physician-population ratios, lead or mercury exposure, or mortality rates of five kinds of cancer.