We report two cases of symptomatic West syndrome with severe respiratory syncytial virus (RSV)-induced bronchiolitis: one was a 9-month-old boy who was hospitalized for shock, and the other was a 15-month-old boy in pre-shock condition. Both cases needed mechanical ventilation for approximately 2 weeks. Seizures from the primary disease worsened in both patients during the infection, and both needed long periods of hospitalization, which resulted in a considerable reduction in their quality of life and that of their families. According to a one-year epidemiological survey of RSV infection conducted in 2004-2005 in Nagano prefecture, 7 of 238 hospitalized RSV cases were found to have basic neuromuscular disorders. Compared to patients with chronic lung disease or other primary diseases, they were older, had higher incidence of mechanical ventilation, and required longer hospitalization. Neuromuscular disorders may thus be an important risk factor for severe forms of RSV infection. Although children with such disorders should be protected from RSV, they are currently excluded from the indication for palivizumab administration as passive immunization against RSV in Japan.