Long-term ambulatory cassette EEG with sphenoidal recording (A/EEG-SP) was performed in 51 patients. Group A comprised 31 patients with a clinical diagnosis of complex partial seizures (CPS), and group B comprised 20 patients suspected of having CPS. In group A, detection of temporal spikes was 27% by routine EEG (R/EEG), 72% by sphenoidal EEG (SP/EEG), 27% by A/EEG with temporal chain montage, and 91% by A/EEG-SP. The highest yield achieved by A/EEG-SP as compared with other EEG recordings was documentation of spontaneous seizures of temporal lobe origin. The detection rate of spontaneous seizures by A/EEG-SP was approximately 30%, and the focal or regional onset of seizures could be determined in 60% of patients. In group B, detection of temporal spikes was 11% by R/EEG, 18% by SP/EEG, and 30% by A/EEG-SP. Spontaneous seizures were recorded by A/EEG-SP in two patients (10%). Thus, A/EEG-SP was more effective than A/EEG in detecting interictal and ictal temporal discharges, and A/EEG-SP was superior to SP/EEG in documenting spontaneous seizures of temporal lobe origin.