Objective: To report the use of wide-area 5-aminolevulinic acid photodynamic therapy to treat numerous basal cell carcinomas (BCCs) and basaloid follicular hamartomas (BFHs). Design: Report of cases. Setting: Roswell Park Cancer Institute. Patients: Three children with BCCs and BFHs involving 12% to 25% of their body surface areas. Interventions: Twenty percent 5-aminolevulinic acid was applied to up to 22% of the body surface for 24 hours under occlusion. A dye laser and a lamp illuminated fields up to 7 cm and 16 cm in diameter, respectively; up to 36 fields were treated per session. Main Outcome Measures: Morbidity, patient response, and light dose-photodynamic therapy response relationship and durability. Results: Morbidity was minimal, with selective phototoxicity and rapid healing. After 4 to 7 sessions, with individual areas receiving 1 to 3 treatments, the patients had 85% to 98% overall clearance and excellent cosmetic outcomes without scarring. For laser treatments, a sigmoidal light dose-response relationship predicted more than 85% initial response rates for light doses 150 J/cm2 or more. Responses were durable up to 6 years. Conclusion: 5-Aminolevulinic acid photodynamic therapy is safe, well tolerated, and effective for extensive areas of diffuse BCCs and BFHs and appears to be the treatment of choice in children.