Occupational accidents in the construction sector are still a major concern with relevant costs at different levels, both individually and socially. We developed and tested two structural equation models to study, from the workers’ point of view, the mediator role of working conditions and safety leadership on the relationship between safety culture and safety performance, in a Portuguese firm. This quantitative and correlational case study applied a questionnaire to a convenience sample of 320 workers. A structural equation modeling analysis showed that safety culture was predominant in predicting safety performance and that working conditions mediated this relationship, but safety leadership did not. The results allow company’s managers gaining certain insights about the role of safety culture, working conditions and safety leadership on safety performance prediction and in the work accidents’ prevention. Furthermore, likely may help to understand what is going on in other firms, in construction sector in Portugal, and to identify problematic areas needing to be addressed.