In the present article, we examine the contribution of working memory (WM) to solution of the nine-dot problem, a classic insight problem. Prior research has generally demonstrated a limited role for WM in the solution of insight problems, which are typically assumed to be solved without conscious planning. However, MacGregor, Ormerod, and Chronicle (2001) proposed an information-processing model that solves the nine-dot problem by relying on a visual WM mechanism, which they term lookahead. In the present research, we examine whether performance on the nine-dot problem is indeed predicted by WM capacity. The results indicated that spatial WM capacity predicted the tendency to draw lines outside the configuration of dots and predicted the solution on a hint-aided version of the problem. Furthermore, within those solving the problem, higher spatial WM capacity was also related to faster solutions. The results support the information-processing model and suggest a more essential role for WM and planning in insight problem solving than has previously been acknowledged.