Atom probe tomography (APT) has been used to study InxGa 1-xAs quantum dots buried in GaAs. The dots have an average base width of 16.1±1.1 nm and height of 3.5±0.3 nm, but a wide range of sizes. APT composition profiles across the dots are similar to a previous study by cross-sectional scanning transmission electron microscopy, but show significant gallium incorporation (average x=0.22±0.01). The direct three-dimensional nature of the APT data also reveals the complex spatial distribution of indium within the dots. Data such as these are vital for optimizing the performance of quantum dot materials and devices.