We reviewed results of SBRT treatment of 138 patients with medically inoperable stage I NSCLC treated during 1996 - 2003 at five different centres in Sweden and Denmark. Mean age was 74 years ( range 56 - 90) with 69 men and 72 women. SBRT was delivered using a 3D conformal multifield technique and a stereotactic body frame. Doses delivered were 30 - 48 Gy (65% isodose at the periphery of planning target volume, PTV) in 2 - 4 fractions. Equivalent dose in 2 Gy fractions (EQD2) was in the range of 50 - 100 Gy. Mean gross tumour volume (GTV) was 39 cm(3) (2 - 436), and planning target volume was 101 cm(3) (11 - 719). Overall response rate (CR, PR) was 61% (84/138). SD was noted in 36% (50/138). During a median follow-up period of 33 months (1 - 107), 16 (12%) local failures occurred, ten of which also included distant metastases. Local failure was associated with tumour size, target definition and central or pleura proximity. Distant metastases occurred in 25% (35/138) of the patients. Ninety-one ( 65%) patients died during follow-up of which 55 patients (60%) died of other causes than lung cancer. Three- and 5-year overall survival was 52 and 26% respectively. Lung cancer specific 3- and 5-year overall survival was 66 and 40% respectively. Fifty nine percent (83/138) of the patients had no side effects. Fourteen patients experienced grade 3 - 4 toxicity according to radiation therapy oncology group (RTOG). EQD2 (> v.s. < 55.6 Gy) showed a statistically significant benefit survival for the higher doses. SBRT for stage I NSCLC results in favourable local control not inferior to fractionated RT and with acceptable toxicity.