A case-control study was performed from January '80 to February '83 in a group of children aged 3 months to 4 years. The aim of this study was to check possible relationships between immunization with anti-diphtheria-tetanus or anti-poliomyelitis vaccine and serious neurological complications. Twenty-nine cases of neurological illness were investigated among children hospitalized in G, Gaslini Institute (Pediatric Hospital) of Genoa. The diagnosis of admission was "coma" or "generalized convulsions". Two matched controls were chosen among children hospitalized in the same Institute with diagnosis different from coma or convulsions. The controls were chosen on the basis of their age (+/- 6 months), date of hospitalization (+/- 1 months) and sex. Furthermore 58 additional controls, represented by non-hospitalized children living in the same area, were selected on the basis of age and sex. The statistical analysis did not show any relationships between immunization with anti-diphtheria-tetanus or anti-poliomyelitis vaccine and severe neurological illness.