The present article investigates the effectiveness of methods traditionally used to distinguish between the emotions of regret and disappointment and presents a new method — the Regret and Disappointment Scale (RDS) — for assessing the two emotions in decision making research. The validity of the RDS was tested in three studies. Study 1 used two scenarios, one prototypical of regret and the other of disappointment, to test and compare traditional methods (“How much regret do you feel” and “How much disappointment do you feel”) with the RDS. Results showed that only the RDS clearly differentiated between the constructs of regret and disappointment. Study 2 confirmed the validity of the RDS in a real-life scenario, in which both feelings of regret and disappointment could be experienced. Study 2 also demonstrated that the RDS can discriminate between regret and disappointment with results similar to those obtained by using a context-specific scale. Study 3 showed the advantages of the RDS over the traditional methods in gambling situations commonly used in decision making research, and provided evidence for the convergent validity of the RDS.