Sixty-eight of 282 neurosyphilitic patients (24.1%) had repetitive adult onset seizures of unknown cause. Serum and CSF FTA-ABS were more accurate diagnostic tests than the non-treponemal serologic tests. The latter tests were reactive in only 54.5% of patients. In addition to standard anticonvulsants, the patients received 20-24 million units procain penicillin G IM during a three week period. The therapeutic failure rate among these patients was 17.3% in contrast to the nonsyphilitic patients who had 21.8-38.6% failure rates. The prognosis of seizures in GPI patients was the worst regardless of the form of treatment. The use of serum and CSF FTA-ABS is recommended as a part of diagnostic evaluation of adult-onset seizure disorders. The use of large doses of penicillin seems to improve the results of treatment.