The aim of this study was to assess the prevalence of opioid-induced dysuria in patients with advanced cancer having pain and to evaluate the possible factors associated. A consecutive sample of cancer patients admitted to an acute pain relief and palliative care unit during 8 months was surveyed. Most patients (147, 86.5%) were receiving opioids at admission. The mean age was 65.1 (SD 12.2) and 106 patients were males. Twenty-five patients presented with dysuria at admission (of which 22 were taking opioids, 14.9%). Eleven patients were inserted a bladder catheter at admission for urine monitoring and 18 patients had urinary incontinence. During admission, 31 patients presented dysuria (19% of population was taking opioids). The prevalence of dysuria was more frequent in males, in patients presenting pelvic masses or who had pelvic surgery, and patients with neurological deficits. Opioid switching during admission was correlated to the occurrence of dysuria. Patients with chronic cancer pain receiving opioid therapy present a prevalence of bladder dysfunction of about 15%, which is influenced by several concomitant factors. Given the complex clinical picture of advanced cancer patients, further studies should be performed to explore the presence of dysuria in patients with no pain and not receiving opioids to know the real weight of opioid therapy with respect to other variables.