The attenuated poliovirus vaccine is remarkably effective in preventing the disease but its innocuity has always been questioned. It seems to be responsible for occasional cases of spinal paralysis occurring in developed countries where poliomyelitis has virtually been eradicated. The authors report two cases of acute anterior poliomyelitis in young adults, in which the poliovirus recovered from the faeces might have been of vaccinal origin. Virological techniques do not always characterize the strains isolated, nor distinguish between a vaccinal mutant and a wild poliovirus. These data, together with previously published cases, have prompted the authors to discuss whether the use of a live poliovaccine is justified.