Children(5-12years)andadolescents(13-19years)withDownsyndrome(DS)possessasetofhealth,anatomical,physiological,cognitive,andpsycho-socialattributespredisposingthemtolimitationsontheirphysicalfitnessandphysicalactivity(PA)capacities.Thepaucityofstudiesandtheirconflictingfindingspreventaclearunderstandingand/orsubstantiationoftheselimitations.Thepurposeofthisarticlewastoreviewthemeasurement,determinantsandpromotionofphysicalfitnessandPAforyouth(i.e.,childrenandadolescents)withDS.TheexistingbodyofresearchindicatesthatyouthwithDS:1)havelowcardiovascularandmuscularfitness/exercisecapacity;2)demonstrateagreaterprevalenceofoverweightandobesity;3)alargeproportiondonotmeettherecommendedamountofdailyaerobicactivity;and4)theirPAlikelydeclinesthroughchildhoodandintoadolescence.Futureresearchshouldfocuson:1)strengthtestingandtrainingprotocols;2)methodologiestodeterminePAlevels;and3)practicalinterventionstoincreasePA.