Intracellular protein deposition due to aggregation caused by conformational alteration is the hallmark of a number of neurodegenerative disorders, including Parkinson's disease, tauopathies, Huntington's disease, and familial encephalopathy with neuroserpin inclusion bodies. The latter is an autosomal dominant disorder caused by point mutations in neuroserpin resulting in its destabilization. Mutant neuroserpin polymerizes and forms intracellular aggregates that eventually lead to neurodegeneration. We generated genetically modified mice expressing the late-onset S49P-Syracuse or the early-onset S52R-Portland mutation of neuroserpin in central nervous system neurons. Mice exhibited morphological, biochemical, and clinical features resembling those found in the human disease. Analysis of brains revealed large intraneuronal inclusions composed exclusively of mutant neuroserpin, accumulating long before the development of clinical symptoms in a time-dependent manner. Clinical symptoms and amount of neuroserpin inclusions correlated with the predicted instability of the protein. The presence of inclusion bodies in subclinical mice indicates that in humans the prevalence of the disease could be higher than anticipated. In addition to shedding light on the pathophysiology of the human disorder, these mice provide an excellent model to study mechanisms of neurodegeneration or establish novel therapies for familial encephalopathy with neuroserpin inclusion bodies and other neurodegenerative diseases with intracellular protein deposition.