Activity of parvalbumin-positive hippocampal interneurons is critical for network synchronization but the receptors involved therein have remained largely unknown. Here we report network and behavioral deficits in mice with selective ablation of NMDA receptors in parvalbumin-positive interneurons (NR1^PVCre−/−). Recordings of local field potentials and unitary neuronal activity in the hippocampal CA1 area revealed altered theta oscillations (5-10 Hz) in freely behaving NR1^PVCre−/− mice. Moreover, in contrast to controls, in NR1^PVCre−/− mice the remaining theta rhythm was abolished by the administration of atropine. Gamma oscillations (35-85 Hz) were increased and less modulated by the concurrent theta rhythm in the mutant. Positional firing of pyramidal cells in NR1^PVCre−/− mice was less spatially and temporally precise. Finally, NR1^PVCre−/− mice exhibited impaired spatial working as well as spatial short- and long-term recognition memory but showed no deficits in open field exploratory activity and spatial reference learning.