Background: Fine needle aspiration (FNA) is the standard to evaluate thyroid nodules for malignancy. The aim of this study was to determine the influence of patient age and gender on the rate of thyroid nodule malignancy by FNA. Methods: A database of 3981 consecutive patients who underwent thyroid FNA between 2002 and 2009 was reviewed. The percentages of benign, indeterminate, and malignant biopsies based on patient age and gender were determined. Statistical analysis was performed using SPSS (SPSS Inc, Chicago, IL). Results: Our patient population included 2766 women (mean age ± SD, 52 ± 15.2) and 964 men (mean age ± SD, 59 ± 13.8). Of the 3722 (93.5%) patients with diagnostic FNAs, 196 (5.3%) had malignant FNA cytology. Malignant FNAs were twice as frequent in patients age ≤45 versus those >45 (8.1% versus 4.0%, P < 0.001). Overall, men had more indeterminate (10.2% versus 6.3%, P < 0.001) and malignant (6.7% versus 4.8%, P = 0.034) FNAs than women. Malignant FNAs in men were greatest in patients over age 45 (6.0% versus 3.2%, P = 0.001). The incidence of malignant FNAs for women peaked in their age 30s (10.4%), whereas the incidence of malignant FNAs for men peaked 10 y later in their age 40s (12.1%). Both men and women had the lowest incidence of malignant FNAs in their age 70s (2.3% and 1.9%, respectively). Conclusions: The typical 5% risk of thyroid nodule malignancy on FNA varies depending on a patient's age and gender. A patient's age and gender should, therefore, be considered when counseling someone of his or her risk of thyroid cancer by FNA. © 2013 Elsevier Inc. All rights reserved.