Lung tumour ablation with a thin-calibre laser applicator system was evaluated. We quantified feasibility, technical success and complication rates in relation to lesion diameter and location. Forty-two patients with 64 lung tumours were treated (39 patients with metastases and three with primary tumours). Mean follow-up was 7.6 months (range 6 weeks to 39 months). Eighty-six percent of treatments were technically successful in the first session. Pneumothorax was the main complication and occurred in 50% of the first 20 patients and in 35% of the rest. Two patients required a chest tube. Fourteen lesions were central and 50 were peripheral. It took several weeks for the effect of the therapy to become apparent on follow-up CT. Thirty-nine percent of all lesions increased in size immediately after treatment. Gross reduction in size with scar formation was seen in 50% of the lesions and cavitation in 13%. Local tumour control was achieved in 51 lesions. Progression after therapy was seen in 9% of lesions <1.5 cm but in more than 11% of larger lesions. Progression was also more frequent in lesions located in the basal parts of the lung (47%). Sixteen patients died due to systemic progression. Our results suggest that successful laser ablation of lung lesions is possible with a miniaturized applicator.