Risk taking is highly prevalent among adolescent males, and a range of studies have shown that decisions become riskier if a peer is present. However, previous studies have typically provided participants with explicit probabilities of risk in each situation. This does not accurately reflect adolescents' real‐world risk taking, where decisions are made in ambiguous situations alongside their peers. Aiming for a more ecologically valid design, the present experiment manipulated situational ambiguity and examined its interplay with group decision making and developmental factors. Adolescent males (N = 202) aged 12–15 completed a “Wheel of Fortune” task and then self‐reported their score, presenting an opportunity to cheat as a measure of antisocial risk taking. As predicted, adolescents were more likely to take risks when probabilities were ambiguous rather than explicit. Further, higher levels of gambling choices were made by groups in ambiguous, but not risk situations. Age significantly predicted gambling in ambiguous conditions, whereas developmental dispositions (risk perception, reward sensitivity, and inhibitory control) did not play a role. Findings provide an insight into the social and situational conditions under which adolescent males engage in reckless behavior.