We define a q-analog of the adjacency matrix of the n-cube, determine its eigenvalues and write down a canonical eigenbasis. We give a weighted count of the number of rooted spanning trees in the q-analog of the n-cube. Remarks on the previous version: The q-analog of the Kac matrix appears in Terwilliger's classification of Leonard pairs and as such its eigenvalues and eigenvectors were known. Reference added to Terwilliger's papers and also to a paper of Johnson. Title changed to reflect this.