Acute primary splenic torsion in dogs is a rare condition with vague presenting signs that requires rapid diagnosis and treatment for successful resolution. A two-year old, spayed female Great Dane presented for collapse following a three-day history of lethargy, vomiting and anorexia. On presentation the dog had a guarded abdomen, was hypotensive and tachycardic with a mild metabolic acidosis, but without other clinical signs and without splenomegaly detected on initial physical examination. Radiographs showed marked splenomegaly and on Doppler ultrasonography veins at the splenic hilus were found to be enlarged, without flow, and containing intraluminal opacities consistent with thrombi. A 360 degree splenic torsion was found at surgery, during which a splenectomy and gastropexy were performed. The dog recovered successfully with minor complications. A review of primary splenic torsions in dogs diagnosed at Cornell between 1981 and 2006 and those described in the literature indicates that German Shepherds, Great Danes, and male dogs are over-represented for the condition.