The microstructure of InxGa1-xN quantum wells with intermediate indium concentrations (x = 0.28 and 0.52) has been studied using transmission electron microscopy. High-resolution lattice images and dark-field images taken under high tilt conditions indicate that the quantum wells are inhomogeneous in character. Most of the area of the quantum wells is pseudomorphic with the GaN adjacent layer. However, misfit dislocations are sometimes observed, although with an inhomogeneous distribution. Strained cluster regions are observed in the high-indium concentration quantum wells, with dimensions ranging from 3 to 10 nm in diameter. Evidence is presented suggesting the extent of clustering depends on the exact orientation of the growth surface which is related to the columnar nature of the GaN/sapphire epitaxy.