We examined the relationship between comorbidity and first return to work after episodes of work-disabling, nonspecific low back pain (NSLBP). An inception cohort of workers with new episodes of NSLBP was identified from administratively maintained occupational health records. We compared 6-month return-to-work rates between workers with one or more comorbid conditions with those without documented comorbidity. Workers with comorbidity were 1.31 times more likely to remain work disabled than those with uncomplicated NSLBP, after adjusting for age, gender, lifting demands, and company membership (adjusted hazards ratio [HR] = 1.31; 95% confidence interval [CI] 1.12 to 1.52). Concurrent injury (i.e., sprains or strains of the neck, upper extremity, and lower extremity; contusions; and lacerations) had the strongest association (adjusted HR = 1.49; 95% CI, 1.21 to 1.83), followed by musculoskeletal disorders (adjusted HR = 1.13; 95% CI, 0.77 to 1.66). Comorbidities should be routinely evaluated at first visit by occupational health professionals to better manage disability associated with LBP.