This is a retrospective review of conjunctival mapping biopsies in patients with periocular sebaceous cell carcinoma. The authors reviewed the biopsy technique and outcomes of 45 patients who had mapping biopsies performed over a 25-year period. A total of 429 biopsies were taken of which 121 (28%) were positive. In terms of patients, 28 of the 45 patients biopsied had at least one positive mapping biopsy, and a further five had intraepithelial involvement limited to the wedge resection of the primary tumour. They found that there was no correlation between the location of the primary tumour and the site of positive conjunctival mapping biopsies. Nor was there a correlation between the size of the mapping biopsy and a positive result. Interestingly there was also no correlation between clinical suspicion of conjunctival involvement and a positive biopsy. The results show that a systematic approach to mapping biopsies should be taken, to cover all regions of the conjunctival surface, irrespective of the type (nodular or diffuse) or location of the primary tumour and the clinical appearance of the conjunctiva. Also of note was the apparent higher recurrence rate in those who had adjunctive treatment with Mitomycin C as opposed to cryotherapy, but the numbers were too small to draw any firm conclusions. The paper gives further evidence for the concept of multifocal, non-contiguous disease, and concludes a systematic approach to mapping biopsies is required.