Intracoronary beta-irradiation is believed to be useful in preventing restenosis after coronary angioplasty or as adjunct therapy of an in-stent restenosis. Intracoronary aneurysms after gamma-irradiation were reported by Condado et al. in 1995, especially after doses higher than 25 Gy and without a centering device. In repeated small trials using intracoronary beta-irradiation no aneurysms were reported at 6 months follow-up. We report the development of a coronary aneurysm at 5 months after intracoronary beta-irradiation and stenting. Intracoronary brachytherapy is a new promising technique although one should be cautious about its possible unknown long-term complications.