We reported an unusual case of bilateral ureter strangulation after perineal hernia repair in a dog. Perineal hernias in dogs most commonly affect older intact males, which comprise more than 80% of affected dogs (Hayes and Wilson, 1977; Hosgood et al., 1995).In the present case, castration was performed 1 year prior to the development of perineal hernia. It is well-known that castration at the time of herniorrhaphy can prevent the recurrence of hernia because of the influence of androgen, which induces relaxation of the pelvic diaphragm (Pirker et al., 2009). However, the cause of this condition remains unclear and is recognized to be multifactorial (Aronson, 2012).Bladder retroflexion has been reported in 18–25% of dogs with perineal hernia (Burrows and Harvey, 1973; Hardie et al., 1983; Hosgood et al., 1995; Brissot et al., 2004). Some of these dogs may show clinical signs due to azotemia, while obstruction of blood flow causing necrosis of the bladder may be rarely observed (Hosgood et al., 1995; Brissot et al., 2004). In the present case, preoperative mild distention of the right renal pelvis was detected at the first presentation, although there was no abnormality in the left upper urinary tract. Preoperative mild strangulation of the right ureter was suspected to result in unilateral obstruction due to fibrous tissue, but complete strangulation was not established. This strangulation may have worsened after manipulation during the first surgery, and resulted in complete obstruction after surgery. This situation has not been observed in previous reports.There are several reports about complications after perineal herniorrhaphy, including postoperative urinary incontinence after cystopexy (Grand et al., 2013), ligation of the proximal urethra during resection of a presumed paraprostatic cyst (Sereda et al., 2002), inadvertent prostatectomy and urethrectomy (Flesher et al., 2016), and persistent urinary incontinence and postoperative urine dribbling (Bilbrey et al., 1990; Brissot et al., 2004). In the present case, bladder neck entrapment by a fibrotic band connected to the degenerated mass-like adipose tissue was observed. This adipose tissue has been identified as the herniated omentum in some cases (Snow, 2016). Considering the potential risk of bladder strangulation by this twisted adipose tissue, it should be resected after careful identification of the surrounding tissues, although there are currently no clear guidelines regarding resection of this tissue.Cystopexy and colopexy were performed to prevent relapse of the hernia and to ensure ease of subsequent procedures, which involved reducing hernial contents into the abdominal cavity. It is possible that ureteral strangulation or fibrous tissue formation was related to these procedures. In this case, however, the fibrous tissue was suspected to have been present before the first surgery, because preoperative distention of the right renal pelvis suggested the presence of some preoperative ureteral obstruction. Because removal of the suture of the cystopexy during the second surgery did not improve strangulation, cystopexy itself may not have been directly related to this complication.In conclusion, the findings from the case suggest that degenerative fat tissue should be resected during perineal hernia repair in dogs, in order to prevent possible bladder strangulation after surgery.