Ruminative coping has been associated with negative outcomes in bereavement. Rather than assuming it to be a problematic confrontation process, researchers have recently suggested rumination to be maladaptive through its links with avoidance processes. The main aim of this study was to examine, for the first time, whether the relationship between ruminative coping and symptoms of complicated grief and depression is mediated by avoidance processes (suppression, memory/experiential avoidance, behavioral avoidance, loss-reality avoidance). A sample of 282 adults (88% female, 12% male), bereaved on average 18 months previously, filled out three questionnaires at 6-month intervals. We assessed symptom levels, grief rumination, and trait rumination at baseline; avoidance processes after 6 months; and symptom levels after 12 months. When controlling for initial symptom levels, experiential avoidance mediated the link between grief rumination and complicated grief, and experiential avoidance and behavioral avoidance mediated the link between grief rumination and depression. Post hoc analyses showed suppression may also mediate the link between grief rumination and symptoms of complicated grief, but not depression. Loss-reality avoidance was no significant mediator of these relationships. This study provides initial evidence that rumination during bereavement increases and perpetuates symptoms of psychopathology, because it is linked with specific avoidance processes. Bereaved individuals with problematic grief and (chronic) rumination may benefit from therapy focused on countering avoidance tendencies.