Although RF ablation is an effective treatment of arrhythmias due to atrioventricular accessory pathways, there are cases refractory to conventional catheter ablation. Irrigated tip catheter ablation causes larger and especially deeper lesions than conventional ablation. This article discusses using irrigated tip catheter ablation in cases of right posteroseptal accessory pathways resistant to conventional ablation. Four consecutive patients with no structural heart disease and symptomatic arrhythmias related to right posteroseptal accessory pathways underwent irrigated tip catheter ablation. Conventional RF ablation had been unsuccessful in at least two procedures at more than one center (in three patients at the authors' center). The irrigated tip catheter (Chilli, Cardiac Pathways Corporation) uses a cooling system that is a closed circuit with a saline solution circulating at 0.6 mL/s. Temperature, power, and impedance were monitored during the RF applications. The procedure was successful in all four cases with no complications. In three of them, only one or two applications were necessary. Patients showed no recurrent arrhythmia during several months of follow-up. The results of the present study suggest that RF ablation using an irrigated tip catheter can be useful (and seems to be safe) for the treatment of some right posteroseptal accessory pathways resistant to conventional ablation.