OBJECTIVE Dysplasia of the vulva and uterine cervix are often multicentric, tend to recur and have mostly to be treated by surgical procedures. The photodynamic laser therapy (PDT) may be an alternative, which selectively destroys neoplastic tissue after topical delta-aminolevulinic acid (ALA) used as a photosensitizer. METHODS We measured the distribution of fluorescence in dysplastic and nondysplastic tissue after topical application of ALA in 27 patients with dysplasia. In 3 vulvar and 2 cervical dysplasias, PDT was performed. RESULTS We could show a selective enrichment of endogenous porphyrins in dysplastic tissues, whereas benign tissue showed no fluorescence. The fluorescence was limited to the mucosa. The heterogeneous fluorescence pattern was influenced by the duration of ALA application. In the treated patients, cytological and clinical parameters showed improvement after use of PDT. The longest recurrence-free interval from treatment up to date is 15 months (range 3-15 months). CONCLUSIONS After first results of penetration studies and clinical follow-up, PDT after topical ALA application seems to be a good alternative to surgical procedures in dysplastic changes of the genital tract.