Fossa navicularis strictures following radical prostatectomy are reported infrequently. We recently experienced a series of fossa strictures following robotic-assisted laparoscopic prostatectomy (RLP). We describe herein our experience to prevent fossa strictures and to determine its etiologic factors. From June 2002 to May 2006, 424 patients underwent robotic-assisted laparoscopic prostatectomy with the da Vinci surgical system. Fossa strictures were diagnosed based on the acute onset of obstructive voiding symptoms and bougie calibration. During our series, we switched from the intra-operative use of an 18 French (F) catheter to that of a 22 F one to avoid inadvertent stapling of the urethra when dividing the dorsal venous complex. After we observed a high incidence of fossa strictures, we reverted back to 18 F catheters during surgery. All patients had an 18 F catheter indwelling for 1 week after surgery. Parameters were evaluated using Fisher's exact test and Student's t-test for means. The 18 F catheter group of patients (n = 293) developed one fossa stricture, whereas the 22 F catheter group (n = 131) developed nine fossa strictures (P < 0.01). The fossa stricture rate in the 18 F group was 0.3% versus 6.9% in the 22 F group. The two groups had no differences in age, body mass index, cardiovascular disease, American Urological Association symptom score, urinary bother score, preoperative prostate-specific antigen, operative time, estimated blood loss, cautery use, prostate size, or catheterization time. Based on these results, a larger urethral catheter size - 20 F versus 18 F - during the intra-operative dissection would appear to increase the risk for fossa stricture by more than 20-fold.