BACKGROUND: Several observation-based risk-assessment tools have been developed in recent decades. Studies reporting their use often focus only on the user, the ergonomist. The influence of context and the attributes of the tools may also affect the use but are factors that are seldom considered. OBJECTIVE: The aim of the present study was to explore the process of risk-assessment assignments and to identify factors influencing the use of research-based observation-based risk-assessment tools among Swedish ergonomists, with a background as reg. physiotherapists, employed in Occupational Health Services (OHS). METHODS: A web-based questionnaire (n = 70) was combined with semi-structured interviews (n = 12). RESULTS: There was limited use of several observation-based risk-assessment tools. Furthermore, the results showed that ergonomics risk-assessment assignments are most commonly initiated reactively and that interventions were seldom evaluated. Factors that influence use are related both to the ergonomist and to the attributes of the tools as well as to contextual factors assigned to authorities, and internal organisations both within occupational health service companies and client companies. CONCLUSION: There was a lack of systematic approaches in ergonomics risks assessment and low use and knowledge of risk-assessment tools. This indicates that there is a need to support OHS companies in implementing systematic tools in their practice.