Spectroscopic evidence strongly suggests that the two quasars 0957 + 56 A and B are images produced by the gravitational lensing of a single distant quasar (at z = 1.41) by a giant elliptical galaxy and its attendant cluster (at z = 0.36)1–6. It has also been suggested that the quasar is an intrinsic variable7,8. I report observations that show a variation of ∼1 mag in both components and behaviour typical of intrinsically variable quasars with similar radio structure. The near constancy of the magnitude difference between the components at several epochs despite overall variations favours all the variations being intrinsic to the quasar and also supports the gravitational lens hypothesis. Recent variations of component B1 limit the time delay between the images to between 2 and 24 yr.