In-stent restenosis (ISR) represents the major limitation of stent implantation. Treatment, although of relative technical ease, is unsatisfactory due to the high incidence of recurrent restenosis. Long ISR lesions are especially prone to restenosis. Vascular brachytherapy (VBT) has emerged as a powerful adjunct therapeutic modality to treat ISR. However, VBT may be less effective in very long, diffuse ISR lesions. The present study investigated serial changes of the extent and distribution of neointima formation after beta-radiation as assessed by intravascular ultrasound (IVUS). Following interventional procedures of long ISR in 30 patients, a 40 mm or 60 mm non-centered 90Sr/90Y seed train was used for VBT. Serial (post radiation (PR) and follow-up (FU)) quantitative coronary angiography (QCA) measurements of minimal lumen diameter (MLD) and late lumen loss (LLL) and intravascular ultrasound measurements (IVUS) of cross-sectional areas of the lumen (L-CSA), stent (S-CSA) and intimal hyperplasia (IH-CSA) were performed and compared with historic controls. LLL (0.34 +/- 0.27 mm; p = 0.196), mean decrease of L-CSA (-1.0 +/- 0.8 mm2; p = 0.024) and mean increase of IH-CSA (0.5 +/- 1.3 mm2; p = 0.038) in long ISR were comparable with previously reported results of short ISR. In conclusion the average changes of lumen and intimal hyperplasia after beta-radiation of long ISR are similar to those of short ISR.