Objective To investigate development of sonographic abnormalities and applications of high-resolution ultrasonography (HRUS) in neurofibromatosis type 1 (NF1). Methods Sixteen asymptomatic or minimally symptomatic NF1 patients underwent HRUS at inclusion and 1 year follow-up. Upper and lower extremity nerves were investigated. Peripheral nerve involvement was graded. Results Plexiform neurofibromas (PNFs) were found in 7 patients (43.8%) at inclusion and 10 (62.5%) at follow-up. All initially identified PNFs were also found at follow-up; additional PNFs were found by extended longitudinal assessment at follow-up. All 3 patients with minor and 7 patients with severe peripheral nerve involvement had similar involvement at follow-up. Mean nerve size change was −0.2 mm 2 (±1.6) and 0.3 mm 2 (±6.2) in patients with minor and severe involvement. Mean PNF size change was −0.1 mm 2 (±9.9). Conclusions HRUS allows qualitative assessment of peripheral nerves, which makes it advantageous as initial imaging technique in suspected neuropathy. Patients with minimal nerve involvement remained so, and might therefore require less follow-up for malignant peripheral nerve sheath tumor (MPNSTs) development. Measured change in PNF size was highly variable. Repeating an extensive standardized HRUS protocol during follow-up thus seems less useful to screen for MPNSTs. Significance HRUS has potential applications as diagnostic and screening tool in NF1.