A knowledge of neck strength is important for developing conditioning protocols and for evaluating the relationship between neck strength and head and neck injury, but very few studies have examined neck strength in relationship to athletic participation. The purpose of this study was to quantify isometric neck strength in collegiate and high school athletes. We hypothesized that (a) male athletes would have significantly greater neck strength than females; (b) collegiate athletes would be significantly stronger than high school athletes; and (c) neck strength would vary significantly with head posture. A total of 149 subjects participated (77 men and 72 women; 90 college and 59 high school level). Flexion, extension, and lateral flexion neck strength were measured in neutral and rotated head and neck postures. Neck strength varied significantly according to participants' sex, age, and posture (p < 0.05). Male college students were stronger than those in all other groups (female college students, male high school students, and female high school students). The average female neck strength was 61, 54, and 56% of the average male neck strength for extension, flexion, and lateral flexion, respectively. High school athletes' neck strength was 75, 68, and 65% of collegiate athletes' neck strength for extension, flexion, and lateral flexion, respectively. On average, neck strength was the greatest for extension compared with other force directions. The subjects showed large variation in neck strength with posture, but in general, there were no consistent trends among the subjects. This finding suggests that those whose neck strength was considerably lower in nonneutral postures may consider training to increase strength in rotated postures. These data provide important baseline information for future studies evaluating injury risk or training protocols.