Objectives: To describe the use and reliability of a numerical scoring system (modified Huddart and Bodenham), for the measurement of maxillary arch constriction in patients born with unilateral cleft lip and palate (UCLP), and to compare and contrast the new scoring system with the current methods of measuring treatment outcome, the Goslon and 5-year-old indices. This retrospective comparison with current recommended standards assessed intra- and inter-rater reliability using the Kappa statistic. Methods: Dental study models of fifty patients aged 5, and fifty patients aged 10, all with nonsyndromic complete UCLP, were used in the study. The 5 and the 10 year models were scored using the 5-year-old and Goslon indices respectively. Four examiners scored all the models using the modified Huddart and Bodenham system. The same examiners repeated the scoring under similar conditions, one month later to allow the calculation of inter- and intra-examiner reliability. Results: The intra-rater reliability weighted Kappa values for the modified Huddart and Bodenham system, indicated a high level of reliability for both the 5 year (0.87: incisors, 0.91: canines, 0.88: molars) and 10 year (0.9: incisors, 0.84: canines, 0.78: premolars/molars) models. The weighted Kappa values measuring inter-rater reliability for all six examiners pairs using the 5 and 10 year models, were above 0.85 and 0.74 respectively. There was a statistically significant correlation between the modified Huddart / Bodenham scores and both the 5-year-old and Goslon scores in all cases (p< 0.001). Conclusions: The modified Huddart / Bodenham system described, provides an objective and reliable assessment of maxillary arch constriction. It has a high degree of correlation with the recommended standards, but is more versatile and sensitive to inter-arch discrepancies.