The introduction of high frequency transducers has considerably improved the application of US in the study of musculo-tendinous diseases. We report a rare case of tendinous metastasis from malignant melanoma. The tumour (high karyokinetic index, Clark level IV) arose 4 years earlier in the dorsal region. The patient was admitted for pain in the left knee. A nodular hypoechoic lesion, 0.8 cm in diameter, poorly marginated, located in the subcutaneous tissue and involving the patellar tendon was identified with ultrasound. Histological examination confirmed the diagnosis.