A 5 year old, female spayed, Standard Poodle was presented to the Emergency and Critical Care Service at Cornell University's Hospital for Animals on August 29, 2008 for a 3-month history of progressive weight loss, intermittent diarrhea, and a recently noted heart murmur. Pertinent physical examination findings included bilaterally bounding femoral pulses, a grade V out of VI left systolic heart murmur, and greater than 10% clinical dehydration. Differentials for her progressive weight loss, diarrhea, and the heart murmur included primary cardiac, gastrointestinal, renal, and/or endocrine disease. Baseline blood work revealed a moderate non-regenerative anemia, a neutrophilia with a lymphocytosis, hypercalcemia, hypoalbuminemia, hyperbilirubinemia, and mildly elevated liver enzyme activity. Results of an adrenocorticotropic hormone (ACTH) baseline value and an ACTH stimulation response test supported primary Addison's (hypoadrenocorticism) disease. Addison's disease is an endocrine disorder that results from deficient production of glucocorticoids (cortisol) and/or mineralocorticoids. In light of the lack of electrolyte abnormalities, this case report exemplifies the glucocorticoid-deficient presentation of primary Addison's disease, the clinical approach to diagnosis, and the variable biochemical abnormalities that can manifest with this disease.