Summary Pain resulting from photodynamic therapy (PDT) of skin cancer was investigated. The study included 69 lesions (60 patients) with different types of skin tumours or precursors. Protoporphyrin IX, which is produced by the topical application of δ-aminolevulinic acid, was used as a photosensitizing agent. Twenty-three of the lesions (19 patients) were examined with a fluorescence imaging system which demarcates the tumour area from the healthy skin and visualizes the contrast between the fluorescence from healthy skin and that from the tumour. EMLA® is used on all patients as part of our routine PDT protocol but despite this the major side-effect of PDT is pain during treatment. There is a large variation in pain intensity experienced by the patients, as measured by a visual analogue scale (VAS). Patients with actinic keratoses experienced more pain than those with Bowen's disease or basal cell carcinoma. The mean VAS score was higher when treating lesions located on the head than when treating lesions on the torso or the extremities. Also, treatment of large skin areas resulted in more pain than treatment of small areas, and men experienced more pain than women. The pain experienced by the patients did not correlate with treatment dose, Fitzpatrick skin type, age or fluorescence intensity.