This paper assesses the impact of changes in union density on the male wage structure in the UK over the period 1982-1993. Using data from the Family Expenditure Survey, we estimate the kernel density of hourly wages for men. Counterfactual densities are then generated to predict how the distribution of wages has changed over time because of the decline in union membership. We find that approximately 20% of the increase in the variance of log wages over the period can be attributed to changes in unionisation. The effect is particularly strong in the latter part of the period. We also present disaggregated estimates of the impact of declining unionisation.