CoKu Tau/4 has been labeled as one of the very few known transition disk objects : disks around young stars that have their inner disks cleared of dust , arguably due to planetary formation . We report aperture-masking interferometry and adaptive optics imaging observations showing that CoKu Tau/4 is in fact a near-equal binary star of projected separation \sim 53 mas ( \sim 8 AU ) . The spectral energy distribution of the disk is then naturally explained by inner truncation of the disk through gravitational interactions with the binary star system . We discuss the possibility that such “ unseen ” binary companions could cause other circumbinary disks to be labeled as transitional .