The purpose of this study was to investigate age-related changes in anthropometric and performance variables in professional baseball players. Baseball players (n = 1157) from several professional baseball organizations were categorized into seven cohorts based upon age. All adolescent athletes were categorized as age group 1 (AG1), while the next five groups (AG2 - AG6) consisted of players 20 - 22 y, 23 - 25 y, 26 - 28 y, 29 - 31 y, and 31 - 34 y, respectively. The final group (AG7) was comprised of athletes 35 y and older. All performance assessments were part of the athlete's normal pre-season training camp testing routine. Field assessments were used to analyze lower-body power, speed, agility, grip strength, and body composition. Players were heaviest between the ages of 29 - 31 (AG5), and their body mass in that age group was 10.1% (p = 0.004) greater than AG1. A 7.0% increase (p = 0.000) in LBM occured between AG1 and AG5. No differences in 10-yd sprint times or agility were seen across any age group or position. A 2.0 s (p = 0.001) slower run time for the 300-yd shuttle was seen between AG4 and AG5 for all positions combined. Elevations in grip strength were seen at AG4 compared to AG1 (p = 0.001) and AG2 (p = 0.007) for all position combined. No other differences were noted. Lower body power was increased for all positions combined from AG1 to AG3 (p = .007). This pattern was similar to that observed in position players, but a 12.4% decrease (p = 0.024) in VJMP was seen between AG7 and AG5 in pitchers. Results of this study indicate that lower body power is maintained in baseball players until the age of 29 - 31, while speed, agility and grip strength are maintained in players able to play past the age of 35. Age-related differences observed in this study suggest that athletes focus on their strength and conditioning programs to extend the length of their professional careers.