Most information on results with radiotherapy (RT) for stage I non-small cell lung cancer (NSCLC) is based on retrospective studies on RT-treated inoperable NSCLC cases. Thus, the role of RT for stage I NSCLC, as a curative modality, has not yet been established. A literature search for studies on stage I non-small cell lung carcinoma (NSCLC) treated by RT alone resulted in 18 papers published between 1988 and 2000. The majority of stage I patients received RT treatment because they were medically inoperable. The main contraindications for surgery were grave impairment of pulmonary function and serious cardiovascular disease. Local recurrence was the most common reason for treatment failure (median value 40%) but varied highly between the studies, ranging from 6.4 to 70%. In contrast with local recurrence, regional failure was not a major problem (0-3.2%). Generally, smaller tumour size, low T-stage and increased dose had a favourable impact on local control and increased local control was followed by increased survival. No serious treatment complications were recorded in the majority of these studies. Overall treatment results were, however, disappointing. The median survival in these studies ranged from 18 to 33 months. The 3- and 5-year overall survival was 34+/-9 and 21+/-8% (mean value+/-1 S.E.), respectively. The cause-specific survival at 3 and 5 years was 39+/-10 and 25+/-9% (mean value+/-1 S.E.), respectively. Dose escalation, in a setting with conformal RT using involved field or stereotactic RT, should be the focus of developmental therapeutic strategies with inoperable stage I NSCLC to improve local control and survival.