Introduction There is uncertainty regarding the trends in occupational injuries (OIs) in Sweden due to a significant and increasing problem with under-reporting to injury registers. Under-reporting, in general, is likely to be exacerbated by the rise in precarious employment (PE), a set of unfavourable employment characteristics that would benefit from formal definition and study. PE and global trends are believed also to affect companies and their commitment to health and safety. The present study attempts to bridge these knowledge gaps and presents a study protocol for planned studies, with three main objectives: first, to review the literature for definitions of PE emphasising those that are multidimensional and operationalise components in routinely collected register data; second, to estimate the under-reporting of OI in Swedish registers and third, using results from the first objective, to conduct large, register-based prospective studies, designed to measure effect sizes and interactions between PE, business performance and OI. Methods and analysis First, a scientific literature review will be conducted, including scientific databases and grey literature. Second, data from two major OI registers will be used to estimate the magnitude of under-reporting using capture-recapture methodology. Finally, all residents aged 18-65 in Sweden with any registered income during 2003-2015 will be included. Data sources encompass Swedish population and labour market registers with linkage to both the main OI register with national coverage and hospital records. Trends in PE and OI will be explored, together with risk of OI associated with PE and business performance. Ethics and dissemination The project has been approved by the Regional Ethics Committee, Stockholm (dnr: 2016/2325-31; 2017/2173-32). Dissemination of study results will include a series of peer-reviewed papers, at least one PhD thesis and one report in Swedish, engaging relevant stakeholders. Results will be presented in national and international conferences and through press releases to mass media.