This paper questions conventional approaches to measuring social welfare through gross domestic product (GDP). This paper is divided into two parts. The first part adopts a systems approach to development and incorporates this into the theory of social choice. The second part operationalises this approach through the development of a cost-benefit adjusted gross domestic product (CBAGDP) social welfare function, which overcomes certain limitations of this traditional measure of development. The CBAGDP is then used to estimate welfare in Thailand. This approach is justified because of its normative values and its plausible results.