Immune-mediated hemolytic anemia (IMHA) is a common cause of severe and often life-threatening anemia in dogs. IMHA can be classified as either primary (idiopathic or autoimmune) if no triggering factor is identified, or secondary if an underlying cause is suspected to have triggered the immune-mediated process. Clinical signs typically associated with IMHA reflect the presence of both anemia (lethargy, weakness, collapse, pale mucous membranes, and a hemic heart murmur) and compensatory responses caused by tissue hypoxia and stimulation of the sympathetic nervous system (tachypnea, tachycardia, and bounding pulses). Diagnostic testing performed in a patient with IMHA can serve many purposes. Determination of an appropriate treatment plan as well as prognosis can be highly reliant on knowing whether the IMHA is a primary or secondary disease process, understanding the unique disease manifestation, and recognizing associated complications.