3D printing, more formally known as additive manufacturing (AM), has the potential to revolutionise the construction industry, with foreseeable benefits including greater structural efficiency, reduction in material consumption and wastage, streamlining and expedition of the design-build process, enhanced customisation, greater architectural freedom and improved accuracy and safety on-site. Unlike traditional manufacturing methods for construction products, metal 3D printing offers ready opportunities to create non-prismatic sections, internal stiffening, openings, functionally graded elements, variable microstructures and mechanical properties through controlled heating and cooling and thermally-induced prestressing. Additive manufacturing offers many opportunities for the construction sector, but there will also be fresh challenges and demands, such as the need for more digitally savvy engineers, greater use of advanced computational analysis and a new way of thinking for the design and verification of structures, with greater emphasis on inspection and load testing. It is envisaged that AM will complement, rather than replace, conventional production processes, with clear potential for hybrid solutions and structural strengthening and repairs. These opportunities and challenges are explored in this paper as part of a wider review of different methods of metal 3D printing, research and early applications of additive manufacturing in the construction industry. Lessons learnt for metal 3D printing in construction from additive manufacturing using other materials and in other industries are also presented.