Intranuclear inclusions have been observed in layer II neurons of rat piriform cortex. These inclusions have the form of a filamentous lattice and resemble those described by others previously. The frequency of lattice‐containing nuclei shows a significant fourfold increase over a period of 3–33 months of age, with the largest increase occurring after 18 months. The incidence of these inclusions is highest in the superficial third of layer II and is significantly greater than what would be expected from the distribution of all neuronal nuclei in layer II. The presence of intranuclear lattices may be related to the high level of electrical activity in piriform cortex, and their increase with age may reflect a long‐term cumulative effect of this activity. Copyright © 1984 Wiley‐Liss, Inc.