Background This study examined the association between types of loss (i.e., sibling or close friend) and relationship quality (i.e., depth and conflict) with complicated grief, depression, somatic symptoms, and world assumptions in bereaved young adults. Methods Participants were 107 young adults aged 17–29 years who were either bereaved or had never experienced a loss. Among bereaved participants, 66 lost a close friend and seven lost a sibling within the past 3 years (M = 1.63 years). Results Nineteen percent of the young adults met criteria for complicated grief and 31% had mild to severe depression. Participants with a deceased sibling reported greater depth in the relationship as compared to those who lost a friend. They were also more likely to have complicated grief (57% versus 15%) and report significantly higher levels of grief, depression, and somatic symptoms. Those who lost a sibling reported a lower sense of meaningfulness and benevolence of the world and self‐worth as compared with those who lost a close friend or had not experienced a loss. Conclusions Complicated grief and depression are common among bereaved young adults. Sibling loss is particularly distressing to young adults, due in part to the high level of relationship depth, and is associated with increased psychological and physical symptoms postloss.