ABSTRACT:A Miniature schnauzer (12 years old, neutered male) was referred for lethargy, anorexia, and oral bleeding. On initial evaluation, severe hyperglycaemia (blood glucose concentration of 34.9 mmol/l), ketonuria, systemic inflammation (fever, panting, left-shift neutrophilia, and a high C-reactive protein level of 980.97 nmol/l, abnormal pancreatic lipase immunoreactivity, and periodontitis were found. With consideration of possible insulin resistance, blood glucose (BG) levels were monitored using a portable glucose meter (q 1-3 h) and a continuous glucose monitoring system (CGMS) for 72 h (three consecutive trials); intensive insulin therapy was initiated using regular insulin (2.2 IU/kg intravenously). The insulin doses needed, based on the nadir, peak, and duration of insulin action from a traditional intermittent glucose curve were higher than those based on the CGMS results. Meanwhile, transient hyperglycaemic and hypoglycaemic periods, occurring between the intermittent measurements, were easily identified with the CGMS. Therefore, insulin resistance and the Somogyi phenomenon are less likely to occur with use of the CGMS than with intermittent BG measurements. By comparing data from a CGMS to those from an intermittent portable BG measurement system, this case report emphasises the importance and usefulness of a CGMS.