We studied clinical and ictal single-photon emission computed tomography (SPECT) features in 14 patients with parietal lobe epilepsy, nine of whom had structural parietal lobe lesions. Thirteen patients had simple partial seizures of somatosensory (eight), psychic (four), and motor (nine) types. Complex partial seizures (CPS) occurred in seven patients; six were psychoparetic (prominent staring, relative immobility) and one had hyperkinetic activity. Seizures lasted 7 to 110 seconds; 99mTc-HMPAO (hexamethylpropylene amine oxime) was injected ictally, 7 to 89 seconds from seizure onset and 0 to 74 seconds (mean, 21.0 +/- 24.4 seconds) before seizure termination. Ictal SPECT demonstrated focal areas of parietal hyperperfusion in all 14 cases and corresponded with sites of the structural lesions. Parietal hyperperfusion was anterior in eight, posterior in four, and diffuse in two. Quantitative analysis revealed increases in parietal side-to-side perfusion ratios on ictal compared with interictal scans of 11 to 51% (mean, 25.5 +/- 14.4%). Ictal SPECT localization correlated with two main clinical seizure patterns: an anterior syndrome characterized by sensorimotor manifestations and a posterior syndrome characterized by CPS of the psychoparetic type. Ictal SPECT is helpful for localization of parietal seizures. Parietal hyperperfusion is discrete and short-lived, demanding true ictal injections for diagnostic studies.