There has recently been increasing appreciation of ancestral effects on cancer genotypes and phenotypes. Consequently, the need has grown for ancestry annotation of cancer-derived molecular data. In response, we created a computational tool termed RAIDS (Robust Ancestry Inference using Data Synthesis). RAIDS is designed to infer genetic ancestry using as input sequence data from a variety of molecular protocols, even in the absence of matching cancer-free genotypes of the patient. Implemented as an R language package, RAIDS is available from the Bioconductor repository. Here we describe functionalities of RAIDS, provide instructions for its installation, give examples of its usage, and explain the interpretation of its output. While RAIDS is being actively developed, the guidance provided here is expected to apply to future refined and expanded versions of this software tool.