OBJECTIVE: To assess the dental arch relationships of children with a complete unilateral cleft lip and palate (UCLP), born consecutively between 1983 and 1987, who had undergone primary cleft repair in the West Yorkshire region of the United Kingdom. The treatment outcome of this UCLP sample was then compared with the results of a previously published intercenter European study. DESIGN: A retrospective study with standardized record collection and blind assessment. SETTING: Regional dental hospital providing secondary and tertiary health care to the local population. PATIENTS: 35 UCLP patients whose primary repair had been performed within West Yorkshire. INTERVENTIONS: Dental casts obtained for each subject within 12 months of their 10th birthday. MAIN OUTCOME MEASURES: The West Yorkshire models were randomly mixed with an anonymous sample of 115 UCLP cases from other cleft centers in the U.K. The dental arch relationships of the 10-year-old models were assessed by applying the Goslon Yardstick. RESULTS: One-third of the West Yorkshire cleft sample were rated as belonging to Goslon group 2 (good result), another third to group 3 (fair result), and the remaining third to groups 4 and 5 (poor/very poor result). Numerically, the results were of a slightly higher standard than that previously published for other U.K. and European cleft centers but were inferior to the treatment outcome of two European centers. No statistically significant differences were found between the outcome results of the West Yorkshire group and the other cleft centers. CONCLUSIONS: These results provide useful baseline data against which progress in achieving improved treatment outcome for West Yorkshire UCLP children can be determined by future research.