PURPOSE: Patients with rheumatoid arthritis (RA) often have comorbidities related to immune dysfunction, however, the timing of comorbidities relative to RA diagnosis and treatment is not clear. We studied personal and family medical history correlates of incident and prevalent RA in women. METHODS: We used a nested case-control design including women in the Agricultural Health Study (AHS). Physician-confirmed cases of RA (n = 135) were matched to five controls each (n = 675) by birth date. We used logistic regression to examine associations between conditions listed in personal and family medical histories and both incident and prevalent RA, as estimated by odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: The risk of incident RA was associated with personal medical history of nonmelanoma skin cancer (OR = 4.4, 95% CI: 1.4-14.1), asthma or reactive lung disease (OR = 3.7, 95% CI: 1.3-10.5), and cataract (OR = 3.3, 95% CI: 1.0-10.8). Personal history of herpes zoster was associated with prevalent RA (OR = 2.4, 95% CI: 1.2-4.8), but not with incident RA. There were no consistent associations between family medical history and RA. CONCLUSIONS: Patients with medical conditions indicating compromised immunity are at increased risk of developing RA. These results may indicate common pathogenesis of an environmental or genetic nature between such diseases.