Today's business environment is characterised by high complexity and competitiveness. Strategic planning has emerged as an essential tool for defining objectives, guiding organisational action and improving performance. The main aim of this research was to analyse the effect of implementing a strategic plan on the success of organisations, based on a sample of 99 medium and large industrial companies located in mainland Portugal. Using a quantitative approach, data were collected through a questionnaire survey, from the System Analysis of Iberian Balance Sheets Database, and analysed using descriptive and inferential statistical techniques. The results show a high level of adherence to strategic planning and a positive perception of its impact on organisational performance. The empirical analysis revealed a significant correlation between the company's performance and the importance attributed to strategic planning, as well as the complexity of the phenomenon. The results suggest that strategic planning contributes to coherence between the company's mission, objectives and results. The study also presents the most commonly used strategic instruments, the motivations for applying them and the main difficulties experienced, pointing to the positive effect on the management and performance of Portuguese industrial organisations.