Background <p>The ventral premammillary nucleus (PMv), situated within the ventrobasal hypothalamus, is sensitive to steroid hormones and is involved in pheromone-responsive circuits. It maintains robust connections with sexually dimorphic nuclei both within and beyond the hypothalamus. Investigations over the past 15 years have suggested the role of the PMv in integrating environmental cues from conspecifics with internal states, thereby facilitating appropriate physiological and behavioral responses during reproductive and agonistic interactions. Neurochemical evidence indicates sexual dimorphism in the PMv of rats; however, comprehensive structural analyses are lacking.</p> Methods <p>After perfusing and processing the brains of male and female rats during the estrus and diestrus phases, we applied stereological methodology in the PMv.</p> Results <p>Males presented significantly greater neuronal volume and quantity than females did across both cycling phases. Neuronal volume in females was notably greater during estrus than during diestrus. However, no dimorphism was detected in overall volume, neuronal density, volume occupied by neurons, or neuropils.</p> Conclusions <p>Given its role as a nexus between nutritional status and reproductive physiology, as well as its involvement in modulating agonistic behavior, including maternal aggression, structural disparities in the PMv between males and females may reflect divergent functional roles, contributing to sex-specific strategies in reproduction and aggression.</p>