Ultra-endurance cycling events, such as the Race Around Ireland (RAI), involve performing periods of intermittent high intensity cycling for extended durations. The ability to maintain a consistently high mean power output whilst in a sleep deprived state is a critical factor in optimising performance. Purpose: To evaluate the effects of acute sleep deprivation, over 24 hours, on a repeat cycling time trial performance. Methods: Six trained male cyclists (mean ± SD: age 33 ± 4 years; height 1.82 ± 0.03 m; mass 79.3 ± 8 kg) were tested on 3 occasions; each testing bout was separated by 7 days, within a 21 day period. During the first test, subjects performed a maximal incremental test on an electromagnetically braked cycle ergometer. Following a standardised recovery period, each subject then completed a baseline 20 minute self-paced maximal performance test (MPT). The subjects subsequently returned on two further occasions to perform two 24 hour trials. During the course of each 24 hour trial the subjects performed a total of 4 MPT's at set time points in either a sleep deprived (SDep) and or sleep normal (SNorm) state using a randomised crossover design. The MPT’s were undertaken at 0 (T1); 8 (T2); 17 (T3); and 24 hours (T4). During the SDep trial subjects accrued no sleep, while during the SNorm trial they were allocated an 8 hour sleep period between T2 and T3. Results: SNorm resulted in a mean sleep duration of 365 ± 38 minutes. No significant differences were found across baseline trials for each of the 3 tests or for the mean cumulative distance covered over the 4 MPT’s (T1-T4) for SDep compared to SNorm. Further analysis of the data revealed a significant decrease in the total distance covered during the MPT at T3 when compared with T2 (13331m ± 1139m vs. 13867m ± 1234m, p<0.05) for the SDep trial. In contrast, no significant differences were observed across trials in the SNorm group. Conclusions: Despite a 4 % decrease in the MPT observed during a time period usually associated with sleep (T2-T3), acute sleep deprivation over 24 hours had no significant impact in overall time trial performance.