This is a phase I dose escalation study of photodynamic therapy (PDT) for the treatment of patients with pre-malignant tumors and superficial microinvasive disease of the anal canal and/or perianal skin. All subjects (a maximum of 12) will be given the photosensitizer Gliolan orally followed by the administration of red light (629-635 nm) to the tumor from a laser. The dose of Gliolan will be 40 mg/kg administered approximately 4-6 hours before light administration. There will be two levels of light dose: 50 and 100 J/cm2, 3-6 patients in each. Patients will be observed for 30 days for the development of DLT. Patients will be followed up for 24 months for additional toxicity and efficacy data collection.