To study affect regulation in adults with unipolar (n=38) and bipolar (n=38) forms of childhood-onset depression (COD), as compared with adults with no history of psychiatric illness (n=60), we examined affective modulation of the startle eyeblink reflex. Participants were subjected to binaural bursts of white noise while viewing pictures designed to elicit pleasant, neutral, or unpleasant affective states. The blink response was recorded from surface electrodes over the orbicularis oculi muscle during and following pictures. Participants rated the valence and arousal of their responses. Unlike control or bipolar groups, the unipolar group displayed a greater startle during the neutral condition than during the pleasant condition, and failed to display an increase in startle during the unpleasant condition. The bipolar group, unlike the unipolar and control groups, displayed a similar startle response after pleasant and unpleasant pictures. Participants with a high number of lifetime depressive episodes displayed a blunted startle response across affective conditions. Groups reported similar subjective responses to affective stimuli. Current affective symptoms and comorbid diagnoses did not influence startle modulation. In unipolar and bipolar forms of COD, unusual affective modulation or maintenance of the startle response, respectively, may reflect underlying deficits in affect regulation.