National guidance recommends that the possibility of abuse should be considered in all young people (aged <18) attending at genitourinary (GUM) clinic. However attendance at clinic by under 18 year olds is common and abuse is rare. Identifying young people at risk of abuse or sexual exploitation is challenging as victims are frequently coerced into secrecy. Various factors such as involvement in services, pregnancy or drug use are thought to be associated with being at risk of abuse or exploitation. Improving the understanding of how these factors are associated with testing and infection patterns for chlamydia would inform the use of testing data as an indicator of abuse. Improved understanding of the association would also inform risk assessment for chlamydia and thus National Chlamydia Screening Program (NCSP) policy. Linkage of detailed information on the characteristics of a large population based birth cohort of young adults in England, the Avon Longitudinal Study of Parents and Children (ALSPAC), to information from the NCSP’s Chlamydia Testing Activity Dataset (CTAD) within a secure anonymised framework can allow the relationship between known vulnerable young people and their patterns of testing for chlamydia to be characterised.