Foals may present to a referral hospital with the primary diagnosis of uroperitoneum (UP), or they may develop UP while hospitalized for other reasons. Historical, physical, laboratory, and diagnostic variables of foals presenting with UP were compared to those developing UP while hospitalized. Emphasis was placed on the presence of electrolyte abnormalities, evidence of sepsis or infection, and development of anesthetic complications during surgical correction of the defect. Foals developing UP while in the hospital frequently had a history of dystocia and presented at a very young age (< 48 hours) with primary clinical signs compatible with intrauterine compromise or presumed hypoxic or ischemic insult with or without sepsis. Foals referred with suspected UP often had additional problems unrelated to the urinary system. These foals had hyponatremia and hyperkalemia on presentation, whereas foals receiving intravenous fluid therapy consisting of a balanced electrolyte solution did not develop the classical pattern of electrolyte abnormalities, yet a similar increase in serum creatinine and, frequently, decreasing urine production were noted. Infection was present in 63% of the foals, and 78% of foals revealed signs suggestive of sepsis or infection. Intrauterine compromise, presumed hypoxia or ischemia, and sepsis may predispose foals to development of UP. Anesthetic complications occurred in 16% of the foals undergoing surgical correction of the defect, although hyperkalemia was only present in half of the foals with anesthetic complications.