This is the third article in a three-part histopathology series by Melanie Dobromylskyj, of Finn Pathologists, and covers margin assessment, why it is important, and how the surgeon and pathologist can work together to achieve the most useful information. It looks at different forms of margin assessment for surgical samples, and their pros and cons, as well as some of the issues pathologists face when trying to assess margins from certain tumour types.