BACKGROUND: While patients with major depressive disorder (MDD) and bipolar disorder (BD) often exhibit aberrant hormones, it is still unknown whether the hormones differ between MDD and BD across the age spectrum. We aimed to investigate the differences in testosterone and stress hormones between depressed patients with MDD and BD in adolescents and adults, and the impact of suicidal ideation on these. METHODS: A total of 432 depressed patients (270 MDD and 162 BD) were recruited, including 177 adolescents and 255 adults. Plasma levels of adrenocorticotropic hormone (ACTH), cortisol (CORT), testosterone (T), and prolactin (PRL) were measured in all patients. Suicidal ideation was assessed by item 3 of the Hamilton Depression Rating Scale. RESULTS: In adolescents, plasma T levels were higher in MDD than in BD (p=0.018), MDD patients with suicidal ideation exhibited higher T levels than BD patients with suicidal ideation (p=0.036), and plasma T levels were associated with diagnosis (OR CONCLUSIONS: There was an age-specific difference in the T and ACTH between depressed patients with MDD and BD. Suicidal ideation was linked to T in adolescents.