Standardised reporting of head and neck cancer resections according to guidelines issued by the UK Royal College of Pathologists was introduced as a routine procedure in 1998. The guidelines include definitions of "mucosal", "deep", "clear", "close" and "involved" surgical margins. This study of routine diagnostic material describes the frequency, type and morphological features of involved margins, and assesses the influence of tumour site and pathological T and N stage. 301 consecutive radical resection specimens for oral/oropharyngeal squamous cell carcinoma assessed according to the guidelines were appraised. 70 resections (23%) had involved margins. The frequency was related to primary tumour site, and pathological T and N stage. Mucosal involvement was evident in 11 resections, bone in 10, and deep soft tissue in 61-12 resections had multiple category involvement. Both anatomical factors and histological "markers" of tumour characteristics influence the status of surgical resection margins.