This paper presents a multiple case study, which was aimed at identifying similarities and differences on how companies of different sizes operate after ERP system go live (post implementation phase). The study has found several differences and similarities and concluded that the differences are caused by the differences in company structures, sizes, financial constraints and decision making processes. Large Enterprises (LEs) often have in-house competence which Small and Medium-Sized Companies (SMEs) usually lack, and this leads to SMEs to depend on external sources, which makes the operations slightly different. SMEs also focus on their technical operations, often disregarding strategic planning, and this leads to higher risks.