Objective: To determine ultrasonographic peripheral nerve involvement in patients with asymptomatic neurofibromatosis type 1 (NF1). Methods: Thirteen asymptomatic and 4 minimally symptomatic patients with NF1 were included in this cross-sectional pilot study to detect asymptomatic abnormalities of the brachial plexus and upper and lower extremity nerves. Patients underwent clinical examination, nerve conduction studies (NCS), and high-resolution ultrasonography (HRUS). Results: HRUS showed abnormalities in 16 patients (94.1%). Neurofibromas were identified in 10 patients (58.8%): localized neurofibromas were found in 3 patients (17.6%), plexiform neurofibromas in 3 (17.6%), and both in 4 (23.5%). In 6 patients (35.3%), only nerve enlargement without an abnormal fascicular pattern was observed. Severe involvement of the peripheral nervous system with multiple plexiform neurofibromas was observed in 7 patients (41.2%), while 4 patients (23.5%) had no or only minor involvement. Both NCS and HRUS were performed on 73 individual nerve segments. In 5.5%, abnormalities were found with both tests; in 50.7%, only with HRUS; and in 1.4%, only with NCS. Conclusions: HRUS frequently showed subclinical involvement of the peripheral nerves in NF1, also when NCS were normal. HRUS findings ranged from normal to widespread peripheral nerve involvement. Because the presence of plexiform neurofibromas and the benign tumor load are risk factors for the development of a malignant peripheral nerve sheath tumor, HRUS may be a useful tool to identify a subgroup of patients who could benefit from regular follow-up.