High body mass index (BMI >or= 25 kg/m2) is associated with increased postmenopausal breast cancer incidence and mortality. However, few studies have explored associations between BMI and direct measures on target tissue. Epithelial cytology was assessed in 62 high-risk perimenopausal and postmenopausal women using random periareolar fine needle aspiration. Masood cytology index scores were significantly higher among women with BMIs >or=25 kg/m2 than in women with BMIs <25 kg/m2 (13.9 +/- 0.42 versus 12.7 +/- 0.29 kg/m2; P = 0.017). Overweight or obese women also had significantly higher random periareolar fine needle aspiration epithelial cell counts compared with those who were normal weight (1,230 +/- 272 versus 521 +/- 185; P = 0.028). These data suggest that overweight in perimenopausal and postmenopausal women is associated with direct cytologic abnormalities within the breast. Further research is needed to confirm these findings and to determine if this potential biomarker is responsive to changes in body weight resulting from diet and/or exercise interventions.