Internationalisation can be crucial to the long-term success of small- to mediumsized businesses, especially since they are expected to show international growth at an early stage. Our research explores whether firms using an opportunistic portfolio approach are more successful in their efforts to internationalise than are firms using the stage and network approaches. Our research may be characterized as a multi-company longitudinal clinical case study using triangulation to analyse data. The sample consists of six Nordic business-to-business, high-technology firms with sales of €100,000 to €10 million. Four of the six firms had significant revenue from the food industry, petrochemicals, pharmaceuticals, bulk and speciality chemicals and the pulp and paper industry. The results indicate that the opportunistic portfolio model provides some explanation of how firms can internationalise successfully.