This is an additional report by a committee appointed by the minister of health of Great Britain in conjunction with the Medical Research Council to report from time to time on matters relating to vaccination. The first report appeared in 1928. The present one gives an account of ninety cases of post-vaccinal encephalitis that occurred in Great Britain in the two years ended Sept. 30, 1929. In twenty-five cases postmortem examination had been made, and the conditions found in each case are related. For comparison there are reports of cases of encephalitis following smallpox, measles and influenza. There are appendixes dealing with other matters concerning vaccination.