Oops, crossed post, mau got it first! So I'll show how to go backwards:

let myNewList = List<int>()

myList |> List.iter myNewList.Add

(My original post:)

You can take advantage of the fact that both List<> and string[] are usable as sequences since they implement IEnumerable<>:

let x0 = Seq.toList "asdasdads"

let xL = new List<int>()

xL.Add(1)

xL.Add(2)

xL.Add(3)

let x1 = Seq.toList xL

-Neil

Use Seq.toList to convert any IEnumerable to an F# list:

let myList = new System.Collections.Generic.List<int>()

myList.Add(3)

myList.Add(6)

myList.Add(9)

let fsList = myList |> Seq.toList