We performed post-mortem examinations of three patients with progressive neurogenic amyotrophy of long duration. One patient had been clinically diagnosed as having sporadic amyotrophic lateral sclerosis (ALS) and two had been diagnosed with progressive spinal muscular atrophy (PSMA). The disease durations were 10, 17 and 20 years, respectively, and all of the patients died of respiratory failure with no artificial respiratory support. In all of the patients, both the upper and lower motor neuron systems were affected; degeneration of the former was definite, but was milder than that usually encountered in sporadic ALS patients, and the histopathology of the latter was identical to that of sporadic ALS. Light microscopy revealed Bunina bodies, which are characteristic of sporadic ALS, in the remaining anterior horn cells of each patient. In addition, ubiquitin-positive skein-like inclusions were also identified, immunohistochemically, in the remaining anterior horn cells of each patient. Neuron counts indicated that the number of neurons was preserved in Clarke's column in these patients, but was significantly reduced in the intermediolateral nucleus, compared with control subjects. Based on these findings, we think that these three patients, with long disease durations, were affected by essentially the same underlying disease process as that of sporadic, classical ALS. Moreover, we question the neuropathological occurrence of sporadic ALS without involvement of the upper motor neuron system, namely, pure PSMA or lower motor neuron disease.