The major aim of this study was to examine the physical fitness of elite Spanish soccer referees in relation to their age. A secondary aim was to assess the population criterion validity of the 12 min running test (12 MRT) against aerobic-fitness laboratory tests. Participants were 45 soccer referees (age 35.5+/-4.4 years, height 178.3+/-5.0 cm, body mass 75.1+/-6.6 kg, body fat 11.3+/-2.15%, VO2(max), 54.9+/-3.9 ml kg(-1) min(-1)) who were enrolled in the Referees Technical Committee of the Royal Spanish Soccer Federation. They were divided into three age groups: young (Y, 27-32 years, n=15), average (A, 33-38 years, n=17) and old (O, 39-45 years, n=13). No age-related effects were observed for VO2(max), 12 MRT or 200 m sprint performance in either the pooled or grouped data. However, age-related performance decrements were observed for 50 m sprint performance and the ventilatory threshold (VT) running speed. Twelve MRT performance was moderately related to VO2(max), (r=0.46, P=0.002), VT (km h(-1)) (r=0.49, P<0.001), and peak treadmill velocity (PTV) (r=0.60, P<0.001). The results showed that older elite-level referees may be able to limit the expected age-related performance decrements in both aerobic and anaerobic performance usually reported for sedentary people. Additionally, these results show that older referees are able to reach physical fitness levels that have been suggested to be appropriate for coping with match demands.