The randomised badger culling trial (rbct) has shown that widespread badger culling in predefined areas of approximately 100 km2 led to a reduction in the number of cattle herds testing positive for bovine tuberculosis (tb) (‘herd breakdowns’), but was associated with an increase in cattle tb in surrounding areas. This study has tried to estimate the trapping efficacy and the level of reduction of the badger population during the initial proactive culls in the rbct. For seven triplets trapping efficacy was estimated between 71 per cent and 85 per cent, and for three triplets between 35 per cent and 46 per cent. Two of the latter triplets had trapping coinciding with harsh climatic conditions. Badger population removal was estimated at 64 per cent to 77 per cent in the former and 32 per cent to 39 per cent in the latter triplets. In most of the treatment areas there was therefore a consistent and substantial reduction in the number of badgers at the end of the initial cull. All the proactive treatment areas were subjected to further culls, and it is therefore likely that greater reductions would have occurred by the end of 2005, when the analysis of cattle herd breakdowns took place.