The aim of this study was to document cancer trial participation since establishment of the Northern Ireland Cancer Trials Network and investigate population and disease factors associated with trial participation. An independent cohort of over 51 000 cancer patients from the Northern Ireland Cancer Registry covering the same population (2007–2012) was linked to a database of 1316 interventional cancer trial participants in a UK region. The primary outcome measure was participation in an intervention clinical trial. Patients were followed up until 31 March 2013. Kaplan–Meier tests and Cox proportional hazard models using person days at risk to allow for death were used to investigate factors associated with trial participation. Multivariate analysis assessed the impact of age, cancer type and stage, distance from the cancer centre (radiotherapy), marital status, deprivation quintile and rurality. Participation was analysed separately for children (<15 years) and young individuals (15–24 years). Trial recruitment increased three-fold with establishment of a network. Participation was the highest for children at 21%, but relatively low at 2.05% for adults, although higher for haematological malignancies (4.5%). Lower likelihood of trial participation in adults was associated with female sex, older age, distance from regional Cancer Centre and stage 1 disease. The introduction of a regional Cancer Trials Network was associated with increased participation; however, trial participation remains relatively low at the population level especially among elderly patients. Linkage of clinical trials and cancer registry database provide an easy mechanism to monitor trial representativeness at the population level.