Carcinoma of the lip is a common cancer of the head and neck area; its incidence is approximately one-quarter that for oral cavity cancers. It occurs most frequently on the lower lip of elderly males. This non-randomized Phase II study aimed to estimate the complete response (CR) rate to Foscan-mediated photodynamic therapy (Foscan-PDT) in patients with primary cancer of the lip, duration of CR, and the tolerability and safety of Foscan-PDT. Twenty-five patients with squamous cell carcinoma (SCC) of the lip (Tis, T1, T2/N0/M0) and Karnofsky status > or = 70 received 0.15 mg/kg Foscan intravenously, followed 4 days later by a single non-thermal illumination of the tumour (light dose 20 J/cm2, irradiance 100 mW/cm2, lambda=652 nm). Response was determined after 12 weeks and mean follow up is 424 days so far. After 12 weeks, 96% of cases (24/25) showed CR, and all CRs were confirmed by biopsy. The most common adverse event was swelling and local pain at the treatment site. Tumour recurrence was observed in two patients 4 and 18 months after PDT. One patient developed a single lymph node metastasis 7 months after therapy. Photosensitivity reactions occurred in five patients. The functional results were excellent in all patients without any signs of limited mouth opening or impaired lip closure. The cosmetic outcome was better than after surgical therapy. Foscan-PDT is an effective treatment modality for small primary tumours of the lips. Foscan-PDT yields complete response rates comparable to those published for surgery or radiotherapy without causing major toxicity. It allows preservation of form and function and does not compromise future treatment options for recurrent, residual or second primary disease.