A 24-item short form of the 96-item Developmental Behaviour Checklist was developed to provide a brief measure of Total Behaviour Problem Score for research purposes. The short form Developmental Behaviour Checklist (DBC-P24) was chosen for low bias and high precision from among 100 randomly selected item sets. The DBC-P24 was developed from epidemiological data in the first three waves of the Australian Child to Adult Development study, and cross validated for groups with autism, fragile X, Prader-Willi, and Williams in this longitudinal study and in cross sectional Dutch, English, and Finnish samples of young people with intellectual disability. The DBC-P24 has low bias and high precision in cross-validation samples and achieves high sensitivity and specificity to full DBC-P based caseness decisions.