BACKGROUND: Cross-cultural comparisons in optimism (O) and pessimism (P) are few. Kuwait and the United States have different languages, situations, history and culture. On this basis, there is good reason to hypothesise that there are significant differences between the two countries in O and P. AIMS: To explore the differences in, and correlates of, O and P in Kuwaiti and American college students. METHOD: Two samples of male and female undergraduates were recruited from Kuwait (N = 460) and the United States (N = 273). Their mean ages were 21.9 +/- 3.0 and 23.2 +/- 6.5, respectively. All respondents completed the Arabic Scale of Optimism and Pessimism (ASOP), the Suicidal Ideation Questionnaire, the Ego-grasping Scale, the Death Obsession Scale, the Kuwait University Anxiety Scale and the Arabic Obsessive-Compulsive Scale. Kuwaitis responded to the scales in Arabic, and Americans responded in English. RESULTS: The ASOP displayed good internal consistency, a meaningful factorial structure and interpretable factors in both countries. It was found that O correlated negatively with the above scale scores, while the correlations of P were positive, indicating the convergent validity of the ASOP. The Kuwaiti mean score on O was significantly lower than the mean of their American counterparts, and vice versa for P. CONCLUSION: The findings are explained in the light of previous results on personality and psychopathology questionnaires in Kuwaiti and American societies. There is a need to investigate O and P in different cultures. Publication Types: Comparative Study Research Support, Non-U.S. Gov't