Lymphangioma, immune-mediated thrombocytopenia (IMT), and von Willebrand's disease (vWD) were diagnosed by histology, hematology, and a coagulation profile in a 14-month-old, female dachshund. Clinical and laboratory findings included ecchymotic inguinolabial swelling, thrombocytopenia, positive platelet factor-3 assay, prolonged buccal mucosal bleeding time, and subnormal von Willebrand factor antigen concentration and factor VIII activity. The IMT resolved with immunosuppressive glucocorticoid therapy. Histologic examination identified lymphangioma which was too extensive for surgical excision. The history and the clinical and laboratory findings were consistent with congenital vWD, although acquired vWD secondary to lymphangioma could not be ruled out.