**1. Introduction**

Both male and female rats produce ultrasonic vocalizations (USVs) in a variety of contexts that hold communicative intent [1–7]. Adult rat USVs can be categorized into two primary types based on affective state and mean frequencies: 1) alarm USVs which are produced during negative affective states with a mean frequency near 22 kHz, and 2) 50 kHz USVs which are produced during positive affective states [1,6,8–10]. Pups produce USVs with an average frequency of 40 kHz to receive care from their dam (female parent) [8,9,11]. Sexual dimorphism is apparent in all three major categories of USVs. Therefore, the purpose of this review paper is to highlight the known sex differences in rat USV production and acoustics as well as laryngeal biological differences between sexes. All ages were included in this review of the literature. This review is focused on sexual dimorphism of the rat larynx and USVs; however, sex differences exist in other rodent species' USVs (e.g., hamsters [12] and mice [13–16]) and sexual dimorphism of USVs is also mediated by sex differences within the central nervous system, not just the larynx [17–19]. Nevertheless, the rat model is widely used to study vocal communication in a variety of contexts such as social environment [1,5,7,9,20–23], neurogenic disorders [24–29], aging [30–35], and pharmacology [36–44], justifying the need for a comprehensive review of the literature attuned to sex differences.
