BACKGROUND: A majority of cancer-bereaved siblings report long-term unresolved grief, thus it is important to identify factors that may contribute to resolving their grief. OBJECTIVE: To identify modifiable or avoidable family and care-related factors associated with unresolved grief among siblings two to nine years post loss. DESIGN: This is a nationwide Swedish postal survey. MEASUREMENTS: Study-specific questions and the standardized instrument Hospital Anxiety and Depression Scale. Primary outcome was unresolved grief, and family and care-related factors were used as predictors. SETTING/PARTICIPANTS: Cancer-bereaved sibling (N = 174) who lost a brother/sister to childhood cancer during 2000-2007 in Sweden (participation rate 73%). Seventy-three were males and 101 females. The age of the siblings at time of loss was 12-25 years and at the time of the survey between 19 and 33 years. RESULTS: Several predictors for unresolved grief were identified: siblings’ perception that it was not a peaceful death [odds ratio (OR): 9.86, 95% confidence interval (CI): 2.39-40.65], limited information given to siblings the last month of life (OR: 5.96, 95% CI: 1.87-13.68), information about the impending death communicated the day before it occurred (OR: 2.73, 95% CI: 1.02-7.33), siblings’ avoidance of the doctors (OR: 3.22, 95% CI: 0.75-13.76), and lack of communication with family (OR: 2.86, 95% CI: 1.01-8.04) and people outside the family about death (OR: 5.07, 95% CI: 1.64-15.70). Depressive symptoms (OR: 1.27, 95% CI: 1.12-1.45) and time since loss (two to four years: OR: 10.36, 95% CI: 2.87-37.48 and five to seven years: OR: 8.36, 95% CI: 2.36-29.57) also predicted unresolved grief. Together, these predictors explained 54% of the variance of unresolved grief. CONCLUSION: Siblings’ perception that it was not a peaceful death and poor communication with family, friends, and healthcare increased the risk for unresolved grief among the siblings.