Abstract Hereditary spastic paraplegia (HSP) is a degenerative neuromuscular disease characterized by progressive lower extremity weakness, spasticity and hyperreflexia. Inheritance of HSP is commonly autosomal dominant, spastin was identified as the defective gene in chromosome 2p-linked autosomal dominant hereditary spastic paraplegia (AD-HSP). In a large American family with AD-HSP, we have identified a novel spastin mutation at a splice-acceptor site in intron 6 (1130-1 g→a) and detected a corresponding aberrant transcript generated from a cryptic splice site. This is predicted to cause a frameshift and premature truncation of the abnormal spastin protein. Our data are the first to confirm that a mutation in an acceptor site in the spastin gene results in activation of a cryptic acceptor site and a translational frameshift. The clinical phenotype of this pedigree is also discussed.