Abstract Objective This study examined bidirectional associations between mother- and father-reported medical responsibility and medical skill mastery in youth with spina bifida (SB). Methods Participants were 140 youth with SB and their parents who participated in three waves of a longitudinal study across four years (ages 8–15 years at Time 1). Mother- and father-report of both medical responsibility and medical skill mastery were used, and age and estimated intelligence quotient were included as covariates, in cross-lagged models. Results The cross-lagged model provided evidence for significant bidirectional associations between mother-reported medical responsibility and skill mastery across time (root mean square error of approximation=0.09, comparative fix index=0.97). These paths showed that higher levels of child responsibility predicted an increase in skill mastery and that higher levels of mastery predicted an increase in child responsibility across time. Moreover, based on mother-report, sharing of responsibility had stronger effects on increases in skill mastery (Time 1 to Time 2 β=.25, Time 2 to Time 3 β=.27) than skill mastery had on increases in child responsibility (Time 1 to Time 2 β=.08, Time 2 to Time 3 β=.07). The only significant cross-lagged path for father-report was from Time 1 skill mastery to Time 2 responsibility (β=.34). Conclusions Mothers perceive a bidirectional relationship between responsibility and skill mastery across time, whereas fathers appear to mainly consider how skills might affect a subsequent increase in responsibility sharing. Thus, it is important to consider both parents’ perspectives when working to increase medical autonomy in youth with SB.