Intraneural extension of soft tissue sarcomas is uncommon; it is most frequently seen in malignant peripheral nerve sheath tumor, but its occurrence is exceptional in synovial sarcoma. We describe a case arising extraneurally within the deep soft tissues of the forearm, which recurred and resulted in above-elbow amputation, revealing an unexpected finding of diffuse intraneural extension of tumor within a macroscopically normal major nerve. Despite macroscopic and microscopically clear soft tissue margins, the neoplasm had "traveled" a significant distance intraneurally to involve the neural resection margin. This feature does not appear to have been described before; it highlights the issue of whether intraneural spread of synovial sarcoma might have been previously underrecognized, and we discuss briefly some practical implications.