This study was designed to compare the effects of wetsuit (WS) to swimsuit (SS) at identical relative velocities in a swimming flume. Thirteen triathletes performed a continuous progressive swimming test and submaximal steady state swimming tests with a WS and with a SS. Maximal oxygen uptake (V˙O2 max) and the associated velocity at which the V˙O2 max was achieved (VV˙O2max) were determined during the continuous progressive tests. Two 5min swims (at 60% VV˙O2max (V 60% ) and 80% VV˙O2max (V 80% )) were then conducted to measure V˙O2 max, blood lactate concentration (LA), rating of perceived exertion (RPE), the energy cost of swimming (Cs), stroke rate (SR) and stroke length (SL). No difference was found in V˙O2 max, but VV˙O2max with a WS was 5.4% higher than with a SS. V˙O2 with a WS was lower than with a SS alone at V 60% , but not at V 80% . Cs with a WS was lower by 14.4% at V 60% and 7.5% at V 80% than with a SS. No differences were found in LA and RPE between suit conditions during both submaximal swims. Wearing a WS did not affect SL, but SR tended to be higher in a WS for both submaximal velocities. These results suggest that the benefits of wearing a WS are not only improvement in swimming performance and propulsion efficiency, but reduction in gross energy consumption in the swimming portion of triathlon races. Furthermore, when wearing a WS, incremental changes in SR rather than SL are associated with improved swimming performance.