The use of opioid analgesics remains the primary therapy for pain control in cancer patients. However, ample evidence persists showing that treatment is still inadequate. This cross-sectional study was carried out during one year in a Brazilian Cancer Hospital to evaluate the impact of opioid use on analgesia and patients' quality of life. The Pain Management Index (PMI), EORTC QLQ.C30 (Quality of Life of Cancer Patients), Karnofsky Performance Status (KPS), Douleur Neuropathique 4 (DN4), and Brief Pain Inventory-Short Form (BPI-SF) were used. A hundred patients with advanced solid tumors and using opioids were included, with 82% of them reporting daily pain with 58% having intense pain. Morphine with a mean dose of 49 Morphine Milligram Equivalent were used by 57% of them, and PMI was negative in 34% of the sample. Neuropathic pain was found in 72% of patients. The pain was related to all BPI variables. Despite the substantial negative impact of pain on QOL, no association was found between the clinical factors assessed and QOL itself. This gap can be related to the persistence of high levels of sub-treatment, depression, and neuropathic pain associated with the use of low doses of opiates and adjuvant medications in the sample.