Background: The Six-Minute Walk Test (6MWT) has been used with clinical and healthy populations to assess functional capacity and cardiovascular fitness. The aim of this study was to determine the test-retest reliability of a modified-6MWT as well as concurrent validity of walk distance with peak oxygen uptake (VO[subscript 2] peak). Method: Participants were 13 adults (males = 7) with intellectual disability aged 18-44 years recruited from Special Olympics, and with no medical contraindications to exercise. The 6MWT was modified to include familiarisation, a 1:1 pacer, and encouragement every 15 s. Each participant performed the graded maximal treadmill test and the modified-6MWT twice. Results: Test-retest reliability of the modified-6MWT was ICC = 0.98, and linear regression revealed that the modified- 6MWT distance was significantly related to VO[subscript 2] peak (R = 0.84, p less than 0.001). Conclusions: The modified-6MWT is easy to administer and score and shows acceptable validity and excellent reliability for assessing cardiovascular fitness in adults with intellectual disability. (Contains 2 tables and 1 figure.)