The article considers actualisation of diagnostics of the marketing system (MS) of an engineering enterprise as the most important sub-system of the enterprise and priority of use of the results of this diagnostics for improvement of development of MS and economic subject in general. It identifies main elements of results of assessment of MS of an engineering enterprise for building a model of its development as an enterprise component in the market competitive environment. It characterises components of analysis of the results: enterprise MS assessment by selected objects of assessment (product, price, sales, promotion, and organisational structure of the marketing system); generalised assessment of MS; detection of influence of latent factors upon the marketing activity; and modelling stable functioning and development of engineering enterprise MS. Quality of these results significantly depends on information provision of the engineering enterprise MS and is a basis for development of a set of measures for increasing efficiency of functioning of the system at the enterprise under conditions of activation of its marketing activity.