Acute pancreatitis is a challenging medical condition, with the potential for high mortality and comorbidity in companion animal patients. The anatomic position and relationships of the pancreas make direct observation of pancreatic pathology difficult, so the diagnosis of pancreatic disease is typically based on the measurement of biochemical markers in serum and imaging studies of the abdomen. The digestive enzymes typically used in the diagnosis of pancreatitis, amylase and lipase, have poor sensitivity and specificity. Recently, pancreas specific lipases have been purified from dogs and cats, leading to the availability of specific immunoassays for these proteins that show great promise in the diagnosis of acute pancreatitis. After the diagnosis of acute pancreatitis is established, there is a need to assess the severity of the disease to give an accurate prognosis for the patient. This article will review currently available methods used to diagnose acute pancreatitis and the ability of these methods to assess accurately the severity of the disease.