BACKGROUND Bile peritonitis is a severe, nonseptic inflammatory response to bile in the peritoneal cavity. It may result from generalized or localized leakage of bile due to spontaneous rupture of the biliary system or as a complication of biliary tract inflammation, obstruction, manipulation, or trauma. Cytologically, bile in abdominal fluid appears as golden-green granular pigment. OBJECTIVE The purpose of this report is to describe the atypical cytologic features of abdominal fluid in 3 dogs with bile peritonitis. METHODS As part of a diagnostic workup, abdominal fluid was obtained from 3 dogs with bile peritonitis and analyzed. In 2 dogs, fluid bilirubin concentration was determined and Hall's bile stain, Alcian blue-periodic acid-Schiff stain, and Mayer's mucicarmine stain were applied to direct smears of the fluid. RESULTS Acellular mucinous fibrillar material in clumps and lakes was the prominent cytologic finding in the abdominal fluid from all 3 dogs. Bile pigment was not observed. Fluid from the 3 dogs contained increased numbers of inflammatory cells, predominantly neutrophils. Total protein concentration ranged from 2.9 to 5.6 g/dL. Fluid total bilirubin concentration was greater than twice that of the concurrent serum bilirubin concentration. Based on results of the special stains, the amorphous material was positive for mucosubstances, but was negative for bilirubin. In all dogs, bile peritonitis originated from a rent in the common bile duct. CONCLUSIONS Bile peritonitis with fibrillar mucinous material in abdominal fluid has not been described previously in dogs. The material was similar to "white bile" observed in humans and experimentally in dogs as a sequela to extrahepatic biliary tract obstruction. When mucinous material is observed in abdominal fluid from dogs and the fluid bilirubin concentration is greater than twice the serum bilirubin concentration, rupture of the extrahepatic biliary tract should be suspected.