A 3.5-year old female Angora guinea pig was examined because of a history of anorexia, abdominal pain and a palpable abdominal mass. Physical examination revealed a round, well defined mass in the cranial abdomen. The abdominal palpation was slightly painful. Ultrasonography showed a round hyperechogenic mass situated in the gastrointestinal tract, presumably the stomach. Abdominal exploratory surgery was performed and a foreign body in the stomach was palpated. Gastrotomy revealed a compact trichobezoar with 4 cm in diameter. The trichobezoar was removed and the postsurgical recovery of the guinea pig was uneventful. Four months after surgery the guinea pig was in good clinical condition. Prophylactic treatment consisted of a changed diet with a higher proportion of hay; additionally, the hair was kept short by the owner and an oral lubricant paste was given with the intention to lower the risk of recurrence.