It was shown previously that a single episode of pentylenetetrazole-induced generalized seizures was accompanied by learning and memory impairments in rodents. The temporal profile of these impairments suggests that their development at least partially was determined by changes in adult neurogenesis. On the other hand, the cannabinoid receptor agonist tetrahydrocannabinol is known for its protective effect versus seizure-induced cognitive impairments. The aim of our present study was to determine whether tetrahydrocannabinol affects the process of adult neurogenesis in the hippocampus, and whether there is a link between tetrahydrocannabinol-induced changes in adult neurogenesis and memory function in rats. We discovered that tetrahydrocannabinol applied at an ultra-low dose (2 µg/kg) at early stages of differentiation contributes to better survival of newly-born cells in the hippocampus. We also established a significant correlation between the number of newly-born cells that survived in the hippocampus after 3 months and the long-term memory in rats. This finding may indicate that the protective effect of tetrahydrocannabinol on young hippocampal cells may participate in its cognitive effect.