This article examines the demographic characteristics of youth who were interviewed on time, located late or lost for a second interview in a three-year study of vulnerable adolescents called the New Zealand youth transitions study. It reports on the results of an analysis to determine whether or not the considerable effort invested in trying to locate these youth three times made a difference to the quality of the data. Chi-Square test, Fisher's exact test and Multivariate Analysis of Variance (MANOVA) were used to analyse the relationship between completion times, demographic factors and key variables of interest to the study (risk, resilience, functional outcomes, service-use history and service quality). Results revealed that both the key variables of interest and demographic factors significantly varied across completion times. Double interaction by age and completion time emerged across specific sub-scales that represented risk and service-use history. This suggests that the effort invested in locating youth was valuable in terms of reducing bias in results and that suitable techniques of handling 'late and lost to follow-up' data are required in order to fully understand the key factors influencing the lives of vulnerable youth.