A Study of the hospital registers of the Limerick Mental Hospital over a period of five years prior to September 12, 1926, reveals the fact that, among an average population of 624, only i case of acute nephritis was recorded. In the three months following that date no fewer than 17 cases of acute inflammation of the kidneys were observed, presenting very interesting problems in ætiology and epidemiology. A consideration of the infective and clinical data of such an unusual outbreak, presenting, as it did, some remark able characteristics, cannot fail to be of interest.