Farmers report more low back pain (LBP) than rural referents. We have previously demonstrated that the difference in reporting rate cannot be fully explained by known risk factors such as physical work exposures, psychosocial factors and lifestyle. Other etiological factors must be involved. In this cross-sectional population-based study, we investigate LBP comorbidity in terms of coexistent symptoms. A total of 1,013 male farmers, 40-60 years old, and 769 matched rural referents participated in an extensive health survey. Information on causes of primary health care and hospital admissions, symptoms, lifestyle factors, physical work exposures and psychosocial factors were gathered through standardized interviews and questionnaires. In the combined farmer-referent group, the prevalence of LBP was associated with musculoskeletal symptoms other than LBP, chest discomfort, dyspepsia, symptoms from eyes, nose and throat mucous membranes, skin problems, work-related fever attacks, and primary care appointments due to digestive disorders. The associations were independent of age, educational level, smoking habits, body mass index, physical work exposures and psychosocial factors. Presence of both respiratory and digestive disorders doubled the LBP prevalence. Significant associations between LBP and digestive and respiratory disorders were revealed, indicating that LBP and these disease entities may have etiological factors in common.