This study tests the hypothesis that problem gamblers are more prone to have irrational beliefs and depressed mood than non-gamblers. Irrational beliefs refer to fallacious opinions about probabilities. Gamblers like to believe that chance games (i.e., roulette and lottery) can be controlled and that the outcome of such games is dependent on the patterns of previous outcomes. The empirical material consists of responses to a survey that 302 individuals have answered. Half of the respondents were deemed to be problem gamblers. The results showed that compared to the controls, the problem gamblers were more inclined to show illusion of control due to their skill and reported more depressive mood. The results are discussed in terms of difficulties to know the “hen and the egg” regarding depressive mood, and in terms of intermittent reinforcement to continue gambling.