The Naval Service has been actively involved in research on occupational stress for almost 10 years. Three cross-sectional studies have been completed during this time period. It has been shown that the prevalence rate of psychological strain amongst personnel is relatively constant at 31-34%. Several smaller studies, of personnel at sea and of the availability of support services have also been completed. In general, the research has shown that the prevalence rate of strain is higher in the NS than in the general population and is comparable to that found in similar uniformed service organisations, such as the Police. Recognising the limitations of cross-sectional research methods, the decision was made, in 2006, to follow a cohort of personnel over a 6-year period in order to gain better understanding of the processes by which work demands impact on psychological health and to determine whether psychological ill-health has an adverse impact on factors such as premature voluntary retirement and medical downgrading. The paper presents the history of the research and some of the work in progress.