OBJECTIVES: An original decision model has shown that methyl-aminolevulinate (MAL) is a cost-effective intervention in AK and better value for money than excision in BCC. The objective of this observational study was to confirm these results in real life in Belgium from a health-care-payers perspective. METHODS: The study was a prospective, multi-centre observational study in which patients meeting criteria for MAL-treatment were followed for 6 months after first application of methyl-aminolevulinate. Clinical response (CR) and cosmetic outcome (CO) were evaluated at the last available visit during the follow-up period. Socio-demographic data, treatment related data and safety data were collected. Inclusion period was October 2004-October 2005. RESULTS: A total of 247 patients were evaluated (mean age:69 years; 53% males). 47% of patients had AK with an average of 7.1 ±0.4 lesions (32% new lesions); BCC-patients had an average of 1.7 ±0.2 lesions (89% new lesions). As the majority of patients had multiple lesions, on average 2.78 tubes of MAL were used per patient. AK patients had a mean of 3.3 dermatologist visits related to diagnosis, treatment and follow-up (BCC: 3.6 visits). In 83% of AK and in 84% of BCC patients, all lesions showed a complete CR. Good to excellent CO was found in 95% and 93% of AK and BCC patients respectively. Total cost of care (MAL-treatment plus follow-up) was €383 in AK and €298 in BCC-patients, with a higher effectiveness compared to the model. The model showed €255 for AK and €303 for BCC. Higher costs in AK were due to a higher mean number of lesions per patient compared to the model population (4.1 lesions per patient). CONCLUSIONS: This observational study confirms the cost-effectiveness shown in the original model for methyl-aminolevulinate in AK and BCC and shows that real-life data can be used to refine original decision models.