Venous leg ulcers (VLUs) are the most common causes of leg ulcers due to venous insufficiency. Most cases persist for more than 6 weeks, referred to as chronic VLUs. These chronic ulcers have been described as a manifestation of Klinefelter syndrome (KS). Platelet-rich fibrin (PRF) is a second-generation platelet concentrate, which contains growth factors required for chronic wound healing. The use of PRF in the management of VLUs in KS has not been reported, to the best of our knowledge. We report a case of chronic VLU associated with KS in a 41-year-old man treated with PRF. Dermatological examination showed a tender, shallow, irregular ulcer partly covered with hard, yellow necrotic tissue on the anterior side of the lower-left leg and hyperpigmented indurated skin on both lower legs. The diagnosis of venous ulcer was established based on clinical manifestation and supported by the result of Doppler ultrasound showed chronic venous insufficiency. Histopathological examination, which showed epidermal acanthosis, dermal fibrosis, and thickening with hemosiderin deposits consistent with the diagnosis of venous ulcer. The patient presented with eunuchoid features characterized by long extremities, gynecomastia, increased fat distribution around the hips, scanty pubic hairs, and small testes. Laboratory tests found decreased levels of testosterone, increased levels of follicle-stimulating and luteinizing hormone, and bilateral testicular atrophy was found from testicular ultrasound. These physical examinations and laboratory findings supported the diagnosis of KS. The patient was treated with PRF dressing once a week. After 7 weeks of treatment with PRF, the ulcer almost reached complete closure. PRF gives a good result in a chronic VLU with KS.