The article contributes to the discussion on the validity and ways of simplifying modern organisations. There is an increasing focus on simplifying organisations, especially their organisational structures. However, the environment of contemporary organisations is increasingly complex, dynamic and uncertain. Therefore, the postulate of simplicity seems to question Ashby’s law stating that one kind of variety must be balanced by a different kind of variety. To cope with the indicated discrepancy, it is assumed that the simplification of some elements of an organisation is only possible due to the excessive complexity of others. The paper aims to verify the concept of organisational simplexity developed by e Cunha and Rego, which postulates the fit between simple structural solutions, complex workforce and complex environment. However, organisational performance is a factor verifying the legitimacy of the fit. The literature study explored the contradiction inherent in the postulate on the simplification of modern organisations. The contingency theory provided a major framework for the study. The research hypothesis was developed and empirically verified. The empirical study targeted 1142 organisations operating in Poland and Switzerland, different by their industry, size and the form of ownership. To verify the hypothesis, a statistical analysis was carried out, and the multiple correspondence analysis (MCA) method was used. The main result of the critical literature analysis is the finding that theoretical indications for simplifying modern organisations are fragmented, mainly focused on simplifying selected elements of an organisation, not considering the contradiction inherent in the postulate of simplicity related to environmental features and not verified empirically. The notion of the simplexity has been adopted, and it treats the simplicity and complexity as interrelated issues conditioned by situational factors. According to the empirical research results, the fit has been revealed between the degree of structure simplicity, the workforce complexity and the environment features.