Background: Childhood cancer is a devastating experience for the family. The objective of the current study was to assess the impact of having a child with cancer on parental separation, divorce, and future family planning among families residing in Denmark. Methods: The authors conducted a nationwide cohort study using Danish registry data. Parents of children diagnosed with cancer between 1982 and 2014 (7066 children and 12,418 case parents) were matched with 10 comparison parents of cancer-free children per case parent (69,993 children and 125,014 comparison parents). We used discrete-time Cox regression models to compare the risk of separation (end of cohabitation) and divorce between case and comparison parents, and to identify risk factors for separation and divorce among case parents only. Descriptive statistics were used to compare family planning between case and comparison parents. Results: Case parents were found to have a slightly lower risk of separation (hazard ratio, 0.96; 95% confidence interval, 0.93-0.99) and divorce (hazard ratio, 0.92; 95% confidence interval, 0.87-0.97) than comparison parents. The authors found that case parents who were aged <45 years, with short education (an International Standard Classification of Education code indicating early childhood education, primary education, and lower secondary education), and who were unemployed were at an increased risk of separation and divorce. Moreover, the parents of children diagnosed with cancer at a young age (aged <15 years) were more likely to separate or divorce. No differences with regard to the total number of children and time to a next child after the cancer diagnosis were observed between case and comparison parents. Conclusions: Having a child with cancer was not associated with an overall adverse impact on parents' risk of separation or divorce and future family planning. These encouraging findings should be communicated to parents to support them along their child's cancer trajectory.