Traditional studies of long-term change in trade union structure have predominantly relied upon the aggregate number of trade unions as the principal measure, or indicator of change over time. Using the Australian trade union movement as an example, this article argues that our understanding of the long-term change in the external structure of trade unions would be better served by using Waddington’s structural events approach examining the incidence of four distinct ‘structural events’–union formations, dissolutions, breakaways and mergers. In doing so, this article presents new data on structural change in the Australian trade union movement between 1969 and 1985. It casts doubt on the traditional argument, which relied on the apparent lack of change in the aggregate number of unions reported by the Australian Bureau of Statistics to argue that this period was one of structural rigidity. The structural events data reveals that far from being a period of structural stability, it was in fact one of significant change, albeit in the composition of the Australian trade union movement, rather than in the aggregate number of trade unions in operation.