Spinde cell sarcomas represent a group of aggressive malignant soft tissue tumors with diverse clinical presentations. While some of these tumors may represent de novo malignant transformation of benign entities, others may present with a long indolent course before their invasive nature is apparent. We report the case of a previously-healthy 73-year-old female with spindle cell sarcoma of the left popliteal fossa who initially presented with a painless mass of several months duration. Magnetic resonance imaging (MRI) suggested a benign vascular lesion/venous angioma, but after the patient’s clinical course changed, repeat MRI eighteen months later was consistent with an infiltrative soft tissue malignancy/sarcoma. Excisional biopsy revealed a stage II spindle cell sarcoma. The patient then underwent radiotherapy and subsequent above the knee amputation. Three years following the above the knee amputation the patient is free of local tumor recurrence or metastatic disease.