Photodynamic therapy (PDT) with topical delta-aminolaevulinic acid (ALA) is considered as a valuable tool for treating non-melanoma skin tumours, but there is no consensus about the methods of treatment, where they should be used and the rates of complete responses. This study reports the treatment of 50 actinic keratoses (AKs), 23 superficial basal cell carcinomas (BCCs), 30 nodular BCCs, 4 pigmented BCCs, 12 superficial squamous cell carcinomas (SCCs), 6 nodular SCCs, 6 Bowen's diseases and 4 keratoacanthomas (KAs). A 20% ALA emulsion was applied under an occlusive dressing for 6-8 h and the skin was then irradiated with 630 nm light from a dye laser. Treatments were delivered every other day until complete clinical disappearance of the lesions was observed. ALA-PDT was interrupted in the case of a partial response if, after two additional treatments, no further improvement was observed. All AKs (50/50), superficial BCCs (23/23), Bowen's diseases (6/6) and KAs (4/4) showed a complete response. In addition, 91.6% (11/12) superficial SCCs, 80.0% (24/30) nodular BCCs and 66.7% (4/6) nodular SCCs responded completely to the treatment. All 4 pigmented BCCs were resistant to the therapy. Some (59) of the treated areas that appeared completely responsive were excised for serial histopathological examination and the remaining 63 were followed-up for 24-36 months (median value, 29 months). Comprehensively, the rates of complete responses decreased after taking into consideration the results of these histological examinations and the long-term follow-up. The final response rates are as follows: 84.0% (42/50) AKs, 86.9% (20/23) superficial BCCs, 50% (15/30) nodular BCCs, 83.3% (10/12) superficial SCCs and 33.3% (2/6) nodular SCCs. The rates of complete responses of Bowen's diseases and KAs remained at 100%.(ABSTRACT TRUNCATED AT 250 WORDS)