Uterine leiomoyomata (fibroids), benign tumors that develop in the majority of women, are the leading indication for hysterectomy in the United States. Although it is well-established that ovarian hormones are involved in fibroid pathogenesis, few studies have examined the role of endocrine disrupting chemicals. This study investigated the relationship of pesticide use and self-reported fibroids among 16,526 women, aged 18-59, in the Agricultural Health Study (AHS). The impact of outcome misclassification from use of self-report was assessed by incorporating estimates of self-report validity. Validity was estimated using self-report of clinical diagnosis and ultrasound findings from Right From The Start (RFTS) (n=2,046) and the Uterine Fibroid Study (UFS) (n=869). Log-binomial regression was used to estimate sensitivity and specificity and examine differences by various factors. Overall sensitivity was [less than or equal to]0.50 in both studies. Sensitivity was higher in blacks than whites (RFTS: 0.34 vs. 0.23; UFS: 0.58 vs. 0.32) and increased with age. Parous white women had higher sensitivity than nulliparae. Specificity was 0.98 in RFTS and 0.86 in UFS. Ethnic differences were modest in UFS (Specificity Ratio, black vs. white: 0.90; 95% confidence interval [CI]: 0.81, 0.99). Parity was inversely associated with specificity among UFS black women (Specificity Ratio: 0.84; 95% CI: 0.73, 0.97). The association between pesticide use and fibroid diagnosis in the AHS was estimated with odds ratios (OR) and 95% CI, adjusting for age and state (Iowa/North Carolina). Ever use of agricultural pesticides was associated with fibroids, with users of [greater than or equal to]3 pesticides having the highest odds compared to never users (OR: 1.31, 95% CI; 1.12, 1.53). Use of any of 10 possible hormonally active pesticides was associated with fibroids when compared with never use of any pesticide (OR: 1.28; 95% CI: 1.12, 1.45). When pesticides were grouped by chemical class, organophosphate users had slightly higher odds than users of other agricultural pesticides (OR: 1.17, 95% CI: 1.05, 1.31). These results suggest a possible association between agricultural pesticide exposure and uterine fibroids that warrants further investigation. Allowing for the imperfect outcome measurement which was demonstrated in the self-report validity analysis resulted in estimates that were further away from the null.