Rationale: Risk factors for asthma among farm women are understudied. Methods: We used polytomous logistic regression to assess pesticide and other occupational exposures as risk factors for adult-onset asthma among 25,814 farm women in the Agricultural Health Study. We used self-reported history of doctor-diagnosed asthma with or without eczema and/or hayfever to create two case groups: atopic and non-atopic asthma. Main Results: At enrollment (1993-7), 702 women (2.7%) reported a doctor-diagnosis of asthma after age 19 (282 atopic, 420 non-atopic). Growing up on a farm (61% of all farm women) was protective for atopic asthma (Odds Ratio (OR)= 0.55, 95% confidence interval (CI)=0.43,0.70) and to a lesser extent for non-atopic asthma (OR=0.83, 95%CI=0.68,1.02, p-for-difference=0.008). Pesticide use was almost exclusively associated with atopic asthma. Any use of pesticides on the farm was associated only with atopic asthma (OR=1.46, 95%CI=1.14,1.87). This association with pesticides was strongest among women who had not grown up on a farm. Women who grew up on farms and did not apply pesticides had the lowest overall risk of atopic asthma (OR=0.41, 95%CI= 0.27,0.62) compared to women who neither grew up on farms nor applied pesticides. Seven of 16 insecticides, two of 11 herbicides, and one of four fungicides were significantly associated with atopic asthma; only permethrin use on crops was associated with non-atopic asthma. Conclusions: These findings suggest that pesticides may contribute to atopic asthma, but not non-atopic asthma, among farm women.