BACKGROUND Klippel-Trenaunay syndrome (KTS) is a congenital vascular malformation with a complicated etiology. It is sporadic and clinically rare in occurrence. The typical characteristics are capillary malformation (also known as port-wine stain), varicose veins and malformations, and bony and/or soft tissue hypertrophy with or without lymphatic malformation, which are known as the “classic clinical triad”. Herein, a rare case of KTS characterized by crossed-bilateral limb hypertrophy accompanied by intermittent hematochezia and hematuria is reported. CASE SUMMARY We described a 37-year-old female with KTS. She was admitted to our hospital owing to the gradual enlargement of the left lower extremity along with intermittent hematochezia and hematuria. The patient was diagnosed to have hemorrhoid bleeding by other hospitals and treated with conventional hemostatic drugs, but continued to have intermittent gastrointestinal bleeding and hematuria. Therefore, she visited our hospital to seek further treatment. During hospitalization, relevant imaging and laboratory examinations and colonoscopy were performed. In combination with the patient’s history and relevant examinations, we considered that the patient had a complex form of KTS. We recommended a combined diagnosis and treatment from the vascular, interventional, anorectal, and other departments, although she declined any further treatment for financial reasons. CONCLUSION The clinical manifestations of KTS are extensive and diverse and chiefly include the typical triad. However, Vascular malformations of KTS can also involve several parts and systems such as digestive and urogenital systems. Therefore, the atypical manifestations and rare complications necessitate the clinician’s attention and are not to be ignored.