A case-control study was performed in women older than 40 yr of age to evaluate the risk of cooking with traditional wood stoves for chronic bronchitis and chronic airway obstruction (CAO). The subjects were recruited from patients attending a referral chest hospital in Mexico City. We selected 127 patients with chronic bronchitis or CAO, of which 63 had chronic bronchitis alone, 23 had CAO alone (FEV1 less than 75% of predicted), and 41 had both chronic bronchitis and CAO (cases). Four control groups were selected: 83 patients with pulmonary tuberculosis, 100 patients with interstitial lung diseases, 97 patients with ear, nose and throat ailments, and 95 healthy visitors to the hospital (controls). Exposure to wood smoke, assessed as any or none, and as hour-years (years of exposure multiplied by average hours of exposure per day) was significantly higher in cases than in controls. Crude odds ratios for wood smoke exposure were 3.9 (95% CI, 2.0 to 7.6) for chronic bronchitis only, 9.7 (95% CI, 3.7 to 27) for CAO plus chronic bronchitis, and 1.8 (95% CI, 0.7 to 4.7) for CAO only. Differences in exposure to wood smoke persisted after adjusting by stratification and logistic regression for age, income, education, smoking, place of residence, and place of birth. Risk of chronic bronchitis alone and chronic bronchitis with CAO increased linearly with hour-years of cooking with a wood stove; odds ratios for exposure to more than 200 hour-years compared with nonexposed were 15.0 (95% CI, 5.6 to 40) for chronic bronchitis only and 75 (95% CI, 18 to 306) for chronic bronchitis with CAO. The findings support a causal role of domestic wood smoke exposure in chronic bronchitis and chronic airflow obstruction.