This article describes clinical, serologic, and histopathologic features of the first North American cohort of patients with positive anti-p200 serology identified at Mayo Clinic, Rochester, Minnesota, USA and Beutner Laboratories, Buffalo, New York, USA. Forty-seven patients were identified with positive p200 laminin beta 4 autoantibodies, detected with either immunoglobulin (Ig)G or IgG4 modified indirect immunofluorescence on HEK293 cells transfected with recombinant laminin beta.