This paper studies the impact of size on labour cost and productivity for Italian manufacturing firms. The distributions of both labour cost and productivity display a wide support, even when disaggregated by sector of industrial activity. Further, both labour cost and productivity, when considered alone, are growing with the size of the firm. We investigate this relationship on a new set of data and we are able to show that once productivity differences among firms have been accounted for, size still retains a positive effect on cost of labour in most of the sectors considered.