There has been a recent increase in public and professional concern about the prescription of strong prescription opioids for pain. Despite this concern, research to date has been limited because of a number of factors such as small sample sizes, exclusion of people with complex comorbidities, and studies of short duration. The Pain and Opioids IN Treatment is a 2-year prospective cohort study of 1500 people prescribed with pharmaceutical opioids for their chronic pain. This article provides an overview of the demographic and clinical characteristics of the cohort using the baseline data of 1514 community-based people across Australia. Participants had been in pain for a period of 10 years and had been on prescription opioids for approximately 4 years. One in 10 was on a daily morphine equivalent dose of ≥200 mg. Employment and income levels were low, and two-thirds of the sample reported that their pain had impacted on their employment status. Approximately 50% screened positive for current moderate-to-severe depression, and 1 in 5 had made a lifetime suicide attempt. There were a number of age-related differences. The younger groups experienced higher levels of pain and pain interference, more mental health and substance use issues, and barriers to treatment, compared with the older group. This study found that the people who have been prescribed strong opioids for chronic pain have very complex demographic and clinical profiles. Major age-related differences in the experiences of pain, coping, mental health, and substance use suggest the necessity of differential approaches to treatment.