Background: Cutaneous squamous cell carcinoma (cSCC) accounts for approximately 20% of all malignant skin tumors and is the second most common skin cancer worldwide. Although the prognosis is generally favorable when diagnosed at an early stage, large tumors with invasion into surrounding tissues and metastasis to regional lymph nodes tend to exhibit more aggressive behavior. In particular, reconstruction of large tissue defects following wide excision of skin tumors remains a significant clinical challenge. Case presentation: We present a rare case of cSCC in a 69-year-old male patient, located on the left hip. The lesion measured 13x9 cm, with well-demarcated borders from the surrounding normal skin, prominently elevated above the skin surface, and characterized by a bluish-brown color. The central superior portion of the lesion was depressed and ulcerated with infiltrative features. Histopathological examination confirmed a well-differentiated, keratinizing invasive cutaneous squamous cell carcinoma. Computed tomography revealed a soft tissue density mass at the skin surface of the left lower abdomen, along with enlargement of the left inguinal lymph nodes. Treatment: The patient underwent wide local excision of the tumor along with regional lymph node dissection (lymphadenectomy). The resulting large tissue defect was reconstructed using an anterolateral thigh (ALT) free flap. During surgery, indocyanine green (ICG) angiography was performed to assess flap perfusion, and handheld Doppler was used to evaluate vascular flow. Results: The postoperative course was uneventful. The flap survived successfully with adequate perfusion. Histopathological examination confirmed negative surgical margins, and no metastasis was identified in the lymph nodes. The patient remains in stable condition without any complaints or symptoms and is under regular follow-up by an oncologist. Conclusion This case demonstrates that combining wide excision with free flap reconstruction is an effective approach for managing large cSCC. In addition, the use of indocyanine green (ICG) angiography for intraoperative assessment of vascular perfusion enhances flap viability and contributes to improved surgical outcomes.