Pain in cancer patients has enormous impact on their quality-of-life. Radiation therapy (RT) is a cornerstone in cancer treatment. The objective of the PREDORT study is to estimate the prevalence of pain in patients attending at Radiation Oncology (RO) Services. A prospective, multicenter study was designed for patients treated at the RO Services of reference hospitals. Patients were seen in their initial Nursing consultation, during which key data was collected, including demographic and comorbidities data, medical history, and oncological and pain characteristics. The study has received approval from the Ethics Committee of Navarra, and all patients signed the Informed Consent. Of the 860 participating patients, 306 reported some type of pain, which implies a prevalence of 35.6%. Of them, 213 identified a cause of oncological origin. The proportion of pain was similar among sexes, but the proportion of non-cancer pain was higher among women (p < 0.05). Regarding pain intensity, the magnitude of breakthrough pain in patients with oncological pain is nearly 1 point greater than in patients with non-oncological pain (7.53 vs 6.81; p = 0.064). Cancer pain is more likely to be limiting of normal life than non-cancer pain (59% versus 38%, p < 0.001). Regarding analgesic treatment, only 60/306 patients (19.6%) were receiving strong opioids. There were 68 patients with pain without any treatment (22.2%). The prevalence of pain in cancer patients referred to RO services is 35.6%, with the prevalence of exclusively oncological pain being 24.8%. Understanding and addressing oncological pain is essential to provide comprehensive care to patients.