Differences in clinical characteristics, symptomatology, and psychiatric comorbidity between early-onset depression (EOD) and late-onset depression (LOD) were examined in a nationwide representative sample. The Korean Composite International Diagnostic Interview was used to investigate psychiatric diagnoses and age of onset. A total of 319 subjects aged 40 years and older with a current major depressive disorder (MDD) were included, and both a continuous and a dichotomous (40 years) age-of-onset indicator were used in the analyses. Despite general similarities between groups, EOD was related to chronic (recurrent and longer episode) and severe (higher lifetime suicidality) clinical features. Hypersomnia and suicidal plans/attempts were associated with EOD, whereas anhedonia was related to LOD. Lifetime generalized anxiety disorder was associated with EOD, whereas dysthymic disorder was related with higher age of MDD onset. This study provides additional evidence of consistent differences between EOD and LOD among middle-aged and older Asians.