Previous epidemiologic studies have revealed that East-Asian populations experience fewer depressive symptoms than American populations do. However, it is unclear whether this difference applies to clinical patients with major depressive disorder (MDD). This present study included 1592 Korean and 3744 American outpatients who were 18 years of age or older and met the Diagnostic and Statistical Manual of Mental Disorders, 4th ed. criteria for single or recurrent episodes of nonpsychotic MDD, and evaluated their symptoms of depression using the Hamilton Depression Rating Scale and the Quality of Life Enjoyment and Satisfaction Questionnaire Short Form. Korean patients scored significantly lower for guilt and depressed mood items, and higher for hypochondriasis and suicidality items than American patients did, after adjusting for total Hamilton Depression Rating Scale scores. Conversely, no significant differences were found in quality and function of daily life between groups. Multivariate logistic regression analyses revealed that Korean patients experienced less frequent depressed mood and guilt, including verbal and nonverbal expression of depressed mood [adjusted odds ratio (AOR)=0.14, 95% confidence interval (CI) 0.08–0.23] and feelings of punishment (AOR=0.036, 95% CI 0.025–0.054) when compared with Americans after adjusting for age and sex. Conversely, Korean patients experienced more frequent suicidality and hypochondriasis, including suicidal ideas or gestures (AOR=2.10, 95% CI 1.60–2.76) and self-absorption of hypochondriasis (AOR=1.94, 95% CI 1.70–2.20). In conclusion, decreased expression of depressed mood and guilt may cause underdiagnosis of MDD in Korean patients. Early diagnosis of and intervention for depression and suicide may be delayed because of this specific cross-cultural difference in depression symptoms.