Back pain and comorbidity are common in older adults. Comorbidity is a promising prognostic factor for the clinical course of backrelated disability, but confirmatory studies assessing its prognostic value are needed. Thus, the aims of this study were to describe the clinical course of back-related disability during 1-year follow-up in patients aged $55 years visiting primary care (general practitioner, physiotherapist, or chiropractor) with a new episode of back pain and assess the prognostic value of comorbidity on back-related disability during 1-year follow-up. A prospective cohort study was conducted, including 452 patients. The outcome measure was Roland-Morris Disability Questionnaire (RMDQ, range 0-24) measured at baseline and at 3-, 6-, and 12-month followup. The Self-Administered Comorbidity Questionnaire was used to assess comorbidity count (CC, range 0-15) and comorbidity burden (CB, range 0-45). The RMDQ scores improved from median (interquartile range) 9 (4-13) at baseline to 4 (1-9), 4 (0-9), and 3 (0-9) at 3, 6, and 12 months, respectively. Using linear mixed-effects models, we found that CC and CB were independently associated with RMDQ scores. A 1-point increase in CC was associated with an increase in RMDQ score of 0.76 points (95% confidence interval [0.48-1.04]) over the follow-up year, adjusted for known prognostic factors. A 1-point increase in CB was associated with an increased RMDQ score of 0.47 points (95% confidence interval [0.33-0.61]). In conclusion, the clinical course of back-related disability for older adults presenting in primary care was favorable, and increased comorbidity was an independent prognostic factor for increased disability levels.