Resistance to radiotherapy is a common issue in prostate cancer treatment with cells surviving treatment being responsible for disease recurrence. Radiotherapy operates by creating DNA lesions which, if left unrepaired, steer cancer cells towards cell death. The problem remains that a subset of cells are capable of repairing DNA breaks and survive treatment, contributing to disease recurrence. While DNA repair has been well characterised, the role of the epigenome in this process is only just beginning to emerge. DNA repair mechanisms must operate within a chromatin context, therefore the distinct epigenetic landscape in a cell may dictate treatment outcome. Loosely packed chromatin is more susceptible to DNA damage while in contrast heterochromatin provides a protective environment. Complicating matters, euchromatin provides ease of access to DNA repair proteins while heterochromatin hinders access. We have previously established an in vitro model of radiation response using 3 prostate cancer cell lines, LNCaP (radiosensitive), 22RV1 (intermediate response) and PC-3 cells (radioresistant)[1]. In order to investigate epigenetic changes following radiotherapy we used this system to profile basal and post-radiation global DNA methylation using the Illumina Infinium 450K arrays. Prostate cancer cells were irradiated at 2Gy and DNA extracted from unirradiated cells and at 1 and 14 days post-treatment. All three cell lines displayed surprisingly stable methylomes with very few changes post-exposure. In terms of basal methylation, the radioresistant PC-3 cells displayed a higher proportion of hypermethylated probes compared to their more radiosensitive counterparts. While further investigation is required, these basal methylation profiles were characteristic for each cell line and may potentially play a role in their varied response to DNA damage or DNA repair capabilities.