The current study provided psychometric information on the parent and child version of the Behavioural Inhibition System (BIS)/Behavioural Approach System (BAS) scale. Parent-child agreement was evaluated (N = 217, 7.5 to 14 years, 50% boys). Moreover, absolute and rank order stability of mother-reported BIS/BAS scores over a 2-year period were assessed (N = 207, 5.5 to 11 years at baseline, 49% boys). Only full measurement invariant (sub-)scales were considered in the parent-child agreement and longitudinal stability assessment. Parent and child ratings were found to be measurement invariant but discrepant on BAS Drive and BAS Reward Responsiveness. In younger children, child ratings on BAS Drive tended to be higher than parent ratings, whereas in older children, child ratings tended to be lower than parent ratings. Further, the discrepancy between the BAS Drive ratings of fathers and children was higher than the discrepancy between the BAS Drive ratings of mothers and children. Finally, the study results suggested 2-year absolute and rank order stability of the measurement-invariant, mother-reported BIS and BAS Drive scores in children aged 5.5 to 11 years at baseline.