Recently the use of small-sided games (mainly 5 vs. 5) proved to be a valid training method to improve aerobic fitness in soccer. Thus, it could be hypothesized that professional futsal (soccer 5-a-side indoor version) players may possess a well-developed aerobic fitness as a consequence of training and game participation. The aim of this study was to examine maximal oxygen uptake (VO2max), ventilatory threshold (VT), and running economy (RE, VO2 at 8 kmxh) of futsal players of different competitive levels to determine whether aerobic fitness is a discriminative variable for futsal success. Subjects were 24 male futsal players from a professional top-ranked second division team (PT, n = 11) and a semi-professional top-ranked third division team (ST, n = 13). Aerobic fitness was assessed with a running protocol performed on a motor-driven treadmill. Professional team and ST players' VO2max were 62.9 +/- 5.3 and 55.2 +/- 5.7 mLxkgxmin, respectively (p < 0.05). RE was 34.1 +/- 2.7 and 32.4 +/- 2.7 mLxkgxmin for PT and ST, respectively (p >0.05). PT and ST attained VT at 70.5 +/- 2.7 and 71.3 +/- 5.2% of VO2max, respectively (p > 0.05). Results showed that VO2max may be considered a competitive-level dependent physical variable in futsal. VO2max values of or above 60 mLxkgxmin are advisable to play futsal at the professional level.