In the standard cosmological model, large-scale structure affects the CMB anisotropies through the integrated Sachs-Wolfe effect. Observations of the ISW effect of individual superstructures of size ~100 Mpc/h at redshifts z~0.5 by Granett et al. show a signal with high statistical significance. However, the amplitude is much larger than expected, and discrepant with the standard LambdaCDM picture at more than 3 sigma even by very conservative estimates. I will discuss the original measurement of the signal and controls for systematic effects, theoretical calculations of the expected value, and comparisons with results from N-body simulations. It is not clear what theoretical models can account for this discrepancy. I will also discuss recent follow-up measurements of the effect, and future tests which may shed some light on its causes.