Objective. The influence of irradiation on the clinical severity of incontinence, sphincter function, morphologic features and short/long-term treatment effects of sphincter training therapy is still insufficiently understood in irradiated patients with fecal incontinence after surgery for colorectal cancer. These parameters were compared in irradiated and non-irradiated patients and followed prospectively with regard to short-and long-term training effects. Material an d methods. Forty-one patients having been irradiated after surgery (50.0 ±5.0 Gy) and 54 non-irradiated patients with fecal incontinence participated in this prospective, non-randomized trial. Baseline evaluation included a semiquantitative severity assessment score of fecal incontinence (modified Cle veland Incontinence Score (MCIS)), rectal manometry and endoscopy. After 3 weeks (short term) of intensive in-hospital pelvic floor exercise combined with biof eedback training, a second evaluation was made. In addition, anal endosonography (EUS) was performed in cases of treatment failure. After one year (long term) a third evaluation was made clinically (MCIS score). Results. Irradiated patients presented with a significantly higher degree of fecal incontinence (lower MCIS) compared to non-irradiated patients: 7.4 ±2.2 versus 8.7 ±2.7 points (p < 0. 001). Rectosigmoidal inflammation was more frequent in irradiated than non-irra diated patients (26.9%versus 9.3%) (p < 0.03). Sphincter pressure, sensation/p ain threshold and the rectoanal inhibitory reflex were similar in both groups. A significant short-term training effect was observed in both groups following s phincter training therapy in terms of an increase in MCIS from 7.4 ±2.2 to 9.4 ±2.7 points in the irradiated group and from 8.7 ±2.7 to 11.4 ±2.5 points in the non-irradiated group (p < 0.0001). After one year the scores were 8.2 ±3.8 and 10.7 ±4.4 points, respectively (p < 0.0001). There was a significant corre lation (p < 0.001)between baseline MCIS and the short-and long-term MCIS. In p atients with short-term treatment failure (16.6%) anal EUS revealed structural defects of the external sphincter in four patients. There was no association of sphincter diameter with sphincter pressure, sensation/pain threshold and short/ long-term MCIS. Conclusions. The main result of this study is that irradiated p atients show short-and long-term training effects comparable with those of non -irradiated patients despite the higher degree of incontinence at baseline. The correlation between the initial MCIS and short-and long-term treatment effect s may be regarded as an important clinical predictor for treatment outcome. Func tional and morphologic features are less suitable for this purpose. Objective. The influence of irradiation on the clinical severity of incontinence, sphincter function, morphologic features and short / long-term treatment effects of sphincter training therapy is still insufficiently understood in irradiated patients with fecal incontinence after surgery for colorectal cancer. These parameters were compared In an irradiated and non-irradiated patients and subsequently prospectively with regard to short-and long-term training effects. Material an d methods. Forty-one patients having been irradiated after surgery (50.0 ± 5.0 Gy) and 54 non-irradiated patients with fecal incontinence participated in this prospective, non-randomized trial. Baseline evaluation included a semiquantitative severity score score of fecal incontinence (modified Cleveland Incontinence Score (MCIS)), rectal manometry and endoscopy. After 3 weeks (short term) of intensive in-hospital pelvic floor exercise combined with biof eedback training, a second evaluation was made. After one year (long term) a third evaluation was made clinically (MCIS score). Results. Irradiated patients presented with a significant higher degree of fecal incontinence (lower MCIS) compared to non-irradiated patients: 7.4 ± 2.2 versus 8.7 ± 2.7 points (p <0.001). Rectosigmoidal inflammation was more frequent in irradiated than non-irra diated patients (26.9% versus 9.3%) (p <0.03). Sphincter pressure, sensation / p ain threshold and the rectoanal inhibitory reflex were similar in both groups. A significant short-term training effect was observed in both groups following s phincter training therapy terms terms an increase in MCIS from 7.4 ± 2.2 to 9.4 ± 2.7 points in the irradiated group and from 8.7 ± 2.7 to 11.4 ± 2.5 points in the non-irradiated group (p <0.0001). After one year the scores were 8.2 ± 3.8 and 10.7 ± 4.4 points, respectively (p <0.0001). There was a significant corre lation (p <0.001) betw een baseline MCIS and the short-and long-term MCIS. In p atients with short-term treatment failure (16.6%) anal EUS revealed structural defects of the external sphincter in four patients. There was no association of sphincter diameter with sphincter pressure, sensation / pain threshold and short / long-term MCIS. Conclusions. The main result of this study is that irradiated p atients show short-and long-term training effects comparable with those of non -irradiated patients despite the higher degree of incontinence at baseline. The correlation between the initial MCIS and short-and long-term treatment effects may may as as an important clinical predictor for treatment outcome. Func tional and morphologic features are less suitable for this purpose.