Pulmonary metastases of renal cell carcinoma are associated with poor prognosis. Systemic interleukin-2 is used to treat pulmonary metastases of renal cell carcinoma; however, its toxicity limits its use. The objective of this study was to evaluate the efficacy and safety of inhaled interleukin-2 in pulmonary metastases of renal cell carcinoma patients. The study was designed as a retrospective chart review in pulmonary metastases of renal cell carcinoma patients treated with inhaled interleukin-2. Between 2000 and 2004, 19 centres in Spain and two in Portugal recruited 51 patients. The treatment schedule was as follows: three cycles of 36 MIU interleukin-2 per day for 5 days/week for 12 weeks (with 1 treatment-free week between cycles) in Spain and for 3 weeks (out of each 4 weeks) for 12 weeks in Portugal. Efficacy was assessed by best response following each treatment cycle and at final evaluation. Kaplan-Meier method was used to estimate progression-free survival and overall survival. Safety data were analysed using descriptive statistics, with toxicities expressed in number of weeks, which were reported. Overall objective response rate was 13.7% (95% confidence interval: 5.7-26.3). Median progression-free survival and overall survival were 8.6 (95% confidence interval: 3.45-16.5) and 23 (95% confidence interval: 11.5-34.5) months. The most common toxicities were cough (40% of cycles) and fatigue (7%). The majority of weeks of toxicities were reported to be only grade 1 or 2 in severity. Inhaled interleukin-2 shows efficacy and mild toxicity of pulmonary metastases of renal cell carcinoma patients, and might be considered as an alternative treatment to the systemic administration of this drug in these patients.