Fourteen survivors of paralytic poliomyelitis experienced new symptoms after years of stability. Seven patients had lost functional capacity, with joint pain, instability and recurrent falls, but were again stable and remained essentially unchanged during a 3-year follow-up period. Seven others had late postpoliomyelitis muscular atrophy (PPMA) with new weakness, wasting, fasciculations and myalgia in muscles originally spared or seemingly recovered. Muscle biopsy from newly affected muscles showed new and chronic denervation with interstitial inflammation in 3 patients. Antibody titers to poliomyelitis virus were not elevated in the CSF, but oligoclonal IgG bands were found in 3 PPMA patients. During the 3-year follow-up period, PPMA patients showed signs of slow progression which continued to be focal. It is concluded that the new symptoms in postpolio patients may be musculoskeletal and relatively stable, or due to a slowly progressive, focal, and apparent benign new motor neuron deterioration.