Adolescents are known for their propensity to take risks, which may be especially strong in social contexts. People are known to use social information more when uncertain of how to decide. How feelings of uncertainty relate to the development of social susceptibility and risky choice across adolescence is unknown. To understand the effects of uncertainty on social influence, we introduce a novel task that measures risky choice under different levels of uncertainty, either with or without observing someone elses advice. Testing 161 adolescents and young adults (10-26 years of age), we show that risky-choice, social information use and subjective uncertainty decrease across development. We also fit a model wherein social information is used to reduce uncertainty to participants’ choices according to Bayesian principles. This model revealed that age-related changes in uncertainty fully accounted for age-related changes in social information use. Our results imply that uncertainty is a key mechanism in adolescents’ social susceptibility in risky behaviour.