Background: Pain in cancer patients is recognized as a major health problem, yet few studies of both inpatient and outpatient populations have been carried out. Objective: The study objective was to assess the frequency, type, and characteristics of pain in adult cancer patients, including both inpatients and outpatients. Methods: This cross-sectional study involved 1064 adult cancer patients (437 outpatients and 627 inpatients) from 44 hospitals and/or long-term-care centers in Catalonia, Spain. Cancer patients suffering from pain of any etiology for >_2 weeks and/or under analgesic treatment >_2 weeks were enrolled. Demographic and pain data were collected. The Spanish version of the Brief Pain Inventory was used to assess pain. Results: Pain frequency was 55.3%. Pain was less frequent in outpatients than inpatients (41.6% versus 64.7%; p<0.001), although median pain duration was longer in outpatients (20 versus 6 weeks; p<0.001). Pain was assessable in 333 patients, and intensity was similar in both out- and inpatients; however, outpatients reported less improvement, less pain interference with daily life, and less pain related to the cancer per se. In both groups, patients with multiple myeloma (73%), breast (65%), and lung cancer (61%) were most likely to report pain. Conclusions: Pain in cancer patients, both ambulatory and hospitalized, remains a challenge for health care professionals, health administrators, and stakeholders. Our study reveals the high level of pain and distress that cancer patients continue to suffer, a problem that is particularly notable in outpatients due to the intensity and duration of the pain.