Underestimation of pneumonia and influenza (P&I) mortality during influenza epidemics was explored in 38 P&U associated deaths among a population of adults during two influenza A (H3N2) epidemics. Pneumonia or influenza was mentioned on 32 (84 per cent) of the death certificates. However, based on rules for assigning cause of death, only nine (24 per cent, SE = 7) and 23 (61 per cent, SE = 8) of the cases would have been included in P&I mortality statistics compiled by the National Center for Health Statistics and the Center for Disease Control, respectively.