Background: This study examines the cross-sectional and longitudinal associations among cognitive variables, depressive symptoms and suicidal ideation in Hong Kong Chinese and Caucasian American adolescents. Methods: Community adolescents (n = 2,044) ages 14-18 years from Hong Kong and the United States provided information regarding their suicidal ideation, depressive symptoms, and cognitions (self-efficacy, cognitive errors and hopelessness), at two surveys, six months apart. Results: Self-efficacy was a weak unique predictor of suicidal ideation in both cultures. Hopelessness was the strongest of cognitive variables in concurrent associations with suicidal ideation in bivariate and multivariate models, in both cultures, and in both boys and girls. Hopelessness continued to offer unique prediction when depressive symptoms were controlled, both concurrently and prospectively. Conclusions: Our results support hopelessness theories of suicidal ideation and behavior in Hong Kong, and extend the cognitive theory of suicidality to a modernized Asian culture.