The offspring of parents with bipolar disorder (OBD) are at higher risk for the development of mental disorders than the offspring of parents with no affective disorder (ONAD). In addition to genetic factors, childhood adversity and a stressful family environment are important risk factors for the OBD. Protective factors in parents, such as social support, may buffer the effects of stress on at-risk children. The present study tested whether parents’ social support and coping style attenuated the relationship between risk status (OBD vs ONAD) and symptoms of mental disorders in offspring. At time 1, when offspring were in middle childhood, parents underwent a diagnostic interview and completed measures of social support and coping style. Sixty nine OBD and 69 ONAD (68 female) between 13 and 29 years old completed a diagnostic interview approximately 10 years later (time 2). As predicted, parents’ social support satisfaction was associated with less substance use disorders (SUDs) symptoms in OBD, but not ONAD (Risk Status X Social Support Satisfaction; F(1, 132)=5.54, p=.02). Unexpectedly, the OBD whose parents reported a larger social network developed more anxiety and depression symptoms than ONAD (Risk Status X Network Size; F(1, 132)=6.24, p=.014). No effects of parents’ coping style were found. Among OBD, having parents with greater social support satisfaction and a smaller social network buffered their development of SUDs and depression and anxiety symptoms by early adulthood. Social support in these high-risk families might have an important protective function for their children’s development.