This article describes a rapid strategic environmental assessment (SEA) of Namibia's Fourth National Development Plan (NDP4) (2012-2013 to 2016-2017). The authors believe this to be the first application of such an approach to a national development plan that typically charts a country's key over-arching development objectives and targets. It was undertaken over four weeks and involved a preparatory desk review of the objectives and implementation strategies of NDP4, Vision-2030 and key sector policies, as well as several other policies. The results were analysed during half-day, facilitated, multistakeholder focus sessions convened for each of five policy clusters that drive development in Namibia: land and agriculture, water, conservation and tourism, mining and industry, and fisheries. Policy performance and synergies/antagonisms within and between policies were assessed, and how policy elements might be improved to enhance synergies/reduce antagonisms and improve their contribution to sustainable development and achieve the goals of NDP4 and Vision-2030. This rapid approach to SEA offers a cost-effective alternative to conventional SEA requiring many months, a team of experts and an extensive process.