Background: Prior research has demonstrated that the presence of regret and unfinished business is associated with poorer adjustment in bereavement. Though there is a growing literature on these constructs among caregivers of adult patients, the literature on regret and unfinished business in bereaved parents has been limited. Aim: The aim of this study was to examine regret and unfinished business in parents bereaved by cancer, as well as their associations with caregiving experiences and prolonged grief. Design: This was a cross-sectional mixed methods study that utilized self-report questionnaires with open-ended items. Setting/Participants: The multisite study took place at a tertiary cancer hospital and pediatric cancer clinical research institution. Participants were 118 parents (mothers = 82, fathers = 36) who lost a child aged 6 months to 25 years to cancer between 6 months and 6 years prior. Results: Results showed that 73% of the parents endorsed regret and 33% endorsed unfinished business, both of which were more common among mothers than fathers ( p ⩽ 0.05). Parents were on average moderately distressed by their regrets and unfinished business, and both regret-related and unfinished business–related distress were associated with distress while caregiving and prolonged grief symptoms. Conclusion: Findings have implications for how providers work with families, including increasing treatment decision-making support, supporting parents in speaking to their child about illness, and, in bereavement, validating choices made. Grief interventions that use cognitive-behavioral and meaning-centered approaches may be particularly beneficial.