Pertussis, or whooping cough, notifications, and deaths declined dramatically after the introduction of mass vaccination in the 1950s, to the extent that many states stopped collecting notifications. However, since 1990, notification rates have increased noticeably from the record low levels seen in the 1970s and 1980s in all Australian states and territories, including NSW. A number of factors, other than a true increase in the underlying incidence of pertussis, may account for this.