Stiff-person syndrome (SPS) is a rare immune-mediated disorder of the central nervous system that is characterized by progressive muscle rigidity and painful spasms in the axial and limb muscles, triggered by external stimuli. This disease has significant phenotypic polymorphism, which significantly complicates timely diagnosis and treatment, aggravating disability. Two clinical examples are presented: a patient with the classic phenotype of SPS and a patient with a focal phenotype — stiff leg syndrome. A feature of these cases was atypical symptoms, which made differential diagnosis difficult.