Enterprise Resource Planning (ERP) systems have mainly been discussed concerning their implementation. A theory-driven, quantitative approach to ERP adoption is rare, especially for Midsized Enterprises (MEs). This paper aims to fill this gap by identifying factors in the areas of technology, organisation and environment, generally known to be part of such managerial decision-making. Nine hypotheses have been derived from literature and tested among Dutch MEs in the electrical, engineering and metal industries. The results of our empirical study show that ERP adoption by MEs is most significantly explained by competitive pressure and the compatibility of the software configuration with the firm's business processes.