BACKGROUND We hypothesized that the factors which may influence health status would differ in patients at different disease stages of chronic obstructive pulmonary disease (COPD). The present study investigated how impairments in health status were distributed in male patients at each disease stage according to the British Thoracic Society (BTS) guidelines, and analysed the contribution of the clinical indices, the dyspnoea rating and the psychological status to the health status of patients at the three disease stages of COPD. METHODS A total of 218 consecutive male patients with stable COPD were recruited from our outpatient clinic. All eligible patients completed pulmonary function testing, progressive cycle ergometry, a dyspnoea rating [Medical Research Council (MRC) dyspnoea scale], an assessment of their anxiety and depression [Hospital Anxiety and Depression Scale (HADS)], and an assessment of their health status [the St. George's Respiratory Questionnaire (SGRQ)]. The patients were categorized into three groups: mild COPD with a FEV1 at 60-79% of the predicted value, moderate COPD at 40-59% of the predicted value, and severe COPD at below 40% of the predicted value. RESULTS Twenty-five patients (11%) had mild COPD, 72 patients (33%) had moderate COPD, and 121 patients (56%) had severe COPD. Significant differences were observed for the total score and for three components on the SGRQ among patients at the three stages (one-way ANOVA, P<0.05). The scores for the total SGRQ and for the activity component were significantly higher for patients with severe COPD than for patients with moderate COPD [Fisher's least-significant-difference (LSD) method, P<0.05], and also significantly higher for moderate COPD patients than for mild COPD patients. The maximal oxygen uptake (VO2 max) correlated significantly with the total SGRQ score in the mild patients [Pearson's correlation coefficient (r) = -0.67], but not in the moderate or severe patients. The MRC dyspnoea scale had strong correlations with the SGRQ in all patient groups (r = 0.53 to approximately 0.70). Anxiety and depression on the HADS showed moderate correlations with the SGRQ score in the mild and severe patients (r = 0.51 to approximately 0.57). Multiple regression analysis showed that in patients with mild COPD, the MRC and VO2 max accounted for the total score on the SGRQ. Anxiety on the HADS plus the MRC scale accounted for the total score on the SGRQ in patients with moderate COPD, and anxiety on the HADS, the MRC scale and the FEV1 significantly influenced the SGRQ severe COPD patients. CONCLUSIONS The disease staging proposed by the BTS guidelines can separate patients with COPD according to impairments in their health status. Furthermore, the factors that influence health status differed in patients at the three disease stages. Our findings support the boundaries used in disease staging and some recommendations from the BTS guidelines.