BACKGROUND: Despite growing evidence and support for shared decision making, little is known about the experiences of parents who hold more active roles than they wish. METHODS: This was a prospective cohort study of 372 parents of children with cancer and their oncologists at 2 academic pediatric hospitals. Parents were surveyed within 12 weeks of the diagnosis, and they were assessed for associated factors and outcomes of holding a more active decision-making role than they preferred. Parents were asked about their preferred and actual roles in decision making. Oncologists were asked to estimate parental preferences. RESULTS: Most parents preferred to share decision making with the oncologist (64% [236 of 372]); however, 13% (49 of 372) preferred oncologist-led decision making. Most parents fulfilled their ideal decision-making role (66% [244 of 372]), but a notable minority were either more involved (14% [52 of 372]) or less involved than they preferred (20% [76 of 372]; P < .0001 [McNemar test]). Oncologists recognized parents' preferred roles in 49% of cases (167 of 341); 24% (82 of 341) of parents preferred more active roles than the oncologist recognized, and 27% (92 of 341) preferred less active roles than recognized. No parent or communication characteristics were found that were associated with parents' holding a more active role than desired in decision making. Parents who held more active roles in decision making than they wished had higher odds of decisional regret (odds ratio, 3.75; 95% confidence interval, 2.07-6.80; P < .0001). CONCLUSIONS: Although many parents fulfill their desired roles in decision making about their child's cancer, some are asked to take on more active roles than they wish. Holding a more active role than desired may lead to increased decisional regret.