BACKGROUND: Necrobiosis lipoidica (NL) is a granulomatous skin disease of unknown origin, and no reliably effective treatment option exists to handle this often disfiguring disease. Recently, a patient with long-lasting NL was reported to be cured by topical photodynamic therapy (PDT). OBJECTIVE: To evaluate the overall potential of PDT in the treatment of NL on the lower legs. METHODS: Retrospective study of 18 patients (aged 16-62 years) from 3 European university departments of dermatology treated with PDT for NL. Methyl aminolevulinate or 5-aminolevulinic acid were used as topically applied photosensitizers. Illumination followed with red light-emitting diode light. RESULTS: Complete response was seen in 1/18 patients after 9 PDT cycles, and partial response in 6/18 patients (2-14 PDT cycles) giving an overall response rate of 39% (7/18). CONCLUSION: Although almost 40% of the cases showed some degree of response, PDT cannot currently be recommended as first-line therapy of NL. Subpopulations of therapy-resistant NL patients may, however, benefit from PDT.