Fundamental and formant frequencies influence perceived pitch and are sexually dimorphic in humans. The information content of these acoustic parameters can illuminate the forces of sexual selection shaping vocal sex differences as well as the mechanisms that ensure signal reliability. We use multiple regression to examine the relationships between somatic (height, adiposity, and strength) and acoustic (fundamental frequency [F0], formant position [Pf], and fundamental frequency variation [F0-SD]) characteristics in a sample of peripubertal Bolivian Tsimane. Results indicate that among males-but not females-strength is the strongest predictor of F0 and Pf and that F0 and Pf are independent predictors of strength when height and adiposity are controlled. These findings suggest that listeners may attend to vocal frequencies because they signal honest, nonredundant information about male strength and threat potential, which are strongly related to physical maturity and which cannot be ascertained from visual or other indicators of height or adiposity alone.