The phenomenon of ‘unknown’ infant deaths addressed in this article was first explored in the course of research on fatalities arising from political violence during the Irish revolution of 1916–1921. Our data are derived from the General Register of Death Indices (G.R.D.I.), held in the General Register Office, Dublin, which are organised alphabetically, and which form an official record of deaths registered either by relatives of the deceased or by medical personnel. When infant ‘unknown’ fatalities were extracted to form a discrete database they showed a curious gender disparity. There were 100 male infant fatalities recorded for every seventy-eight females in the thirty-two counties over the five-year period. On extending the study to 1932, the same ratio was prevalent in the overall dataset of 895 ‘unknown infants’ drawn from the G.R.D.I. (a dataset which excludes the six counties of Northern Ireland for the period from1922). Initial research into the gender imbalance opened out wider questions concerning social mores regarding illegitimacy, and the extent of medical and lay knowledge of how newborn infants might be brought to death.