The present study evaluated the efficacy of a clinician-guided Internet-delivered cognitive behaviour therapy (iCBT) program, the 'Pain Course', to reduce disability, anxiety, and depression associated with chronic pain. Sixty-three adults with chronic pain were randomised to either a Treatment Group or waitlist Control Group. Treatment consisted of 5 iCBT-based lessons, homework tasks, additional resources, weekly e-mail or telephone contact from a Clinical Psychologist, and automated e-mails. Twenty-nine of 31 Treatment Group participants completed the 5 lessons during the 8-week program, and posttreatment and 3-month follow-up data were collected from 30/31 and 29/31 participants, respectively. Treatment Group participants obtained significantly greater improvements than Control Group participants in levels of disability, anxiety, depression, and average pain levels at posttreatment. These improvements corresponded to small to large between-groups effect sizes (Cohen's d) at posttreatment for disability (d = .88), anxiety (d = .38), depression (d = .66), and average pain (d = .64), respectively. These outcomes were sustained at follow-up and participants rated the program as highly acceptable. Overall, the clinician spent a total mean time of 81.54 minutes (SD 30.91 minutes) contacting participants during the program. The results appear better than those reported in iCBT studies to date and provide support for the potential of clinician-guided iCBT in the treatment of disability, anxiety, and depression for people with chronic pain.