One behavioral tactic that juvenile mammals can use to resolve conflict with adults is the reversion to behaviors of an earlier developmental stage. Therefore, we examined the appearance, body posture, and ontogenetic differences of submissive crouch behavior between juvenile male and female guanacos from birth to 9 months of age in Torres del Paine National Park, Chile. On average, submissive crouches appeared 73 days after birth, and juvenile males displayed them more frequently than did juvenile females. Juvenile males also displayed more extreme body postures during submissive crouches than did juvenile females. Sex, group size, and season significantly influenced a juvenile's likelihood of displaying a submissive crouch.