Convulsions or status epilepticus in 11 infants after pertussis vaccination are reported. In 3 cases grand mal epilepsy persisted and 2 children developed infantile epileptic encephalopathy (Lennox syndrome). On the basis of our own experience, the incidence of seizures approximates 1:4800 infants vaccinated or 1:12 800 vaccinations. According to a recent prospective study from the USA, the incidence of seizures may be closer to 1:600 infants. Since there is a significant difference between the incidence of spontaneous fits in children of the same age group and the incidence after vaccination, a causal relationship between the seizures and vaccination appears to be confirmed. The following conclusions are drawn from these observations: 1. In view of the usually benign course of whooping cough today, current vaccination against pertussis is hardly satisfactory. Improvement of the available vaccines is an urgent necessity. The protection should include the population most at risk, i.e. infants during the first few months of life. 2. Parents should be better informed about the risks involved in pertussis vaccination. 3. Booster inoculations should be abandoned. 4. Health authorities should decide whether the current pertussis vaccination program should be continued. 5. Complications following vaccination should be registered at a national centre.