Background: The preferential accumulation of 5-aminolaevulinic acid (ALA)- induced protoporphyrin IX (PpIX) in neoplastic cells supports its potential use in the photodetection of porphyrin fluorescence in tumour cells. Hence, epithelial tumours, including basal cell carcinoma (BCC), might be visualized using the fluorescence of selectively accumulated ALA-induced PpIX. Aim: We evaluated the clinical efficacy of PpIX fluorescence images produced by fluorescence diagnosis (FD) to define the lateral border between the tumour and tumour-free areas of BCC.Methods: Twenty-seven patients with BCC were included. The tumour area was determined 3 hours after application of 20 % 5-ALA cream by Dyaderm digital system. Subsequently, BCCs were excised according to the complete area defined by FD using Mohs micrographic surgery (MMS).Results: The FD tumour margin coincided with the histological tumour margin in 12 cases (44.44%). Conclusion: FD of BCC maybe beneficial, when used as a guide to the safety margin needed before standard surgical excision or MMS.