This paper reports the results of an extensive empirical investigation on the role of project scale (reflected in consortium size and in project budget) on various performance dimensions of publicly funded collaborative research and development (R&D) projects. Recent trends in European research policy are founded on the premise that such scale economies do exist, hence the emphasis placed on the critical mass of R&D projects. We argue that large scale in collaborative R&D confers both positive and negative effects, and thus we hypothesize an inverse U-shaped relation between scale and performance. We only find an inverse U-shaped effect of consortium size on networking impacts and a U-shaped effect of project budget on goal achievement. No other statistically significant relationships were found for the remaining performance dimensions (i.e. scientific outputs, technological outputs, and research capacity impacts). More generally, and consistent with recent work on the relation between quality and quantity in academic research, our analyses offer little evidence to support the idea that increasing scale generally improves collaborative R&D performance. It appears that the simple assumption ‘bigger is better’ in European Union-financed collaborative R&D may need to be reconsidered.