C# Definition:

/// <summary>
/// Represents possible values returned by the MessageBox function.
/// </summary>
public enum MessageBoxResult : uint
{
    Ok = 1,
    Cancel,
    Abort,
    Retry,
    Ignore,
    Yes,
    No,
    Close,
    Help,
    TryAgain,
    Continue,
    Timeout = 32000
}

VB.NET Definition:

''' <summary>
''' Represents possible values returned by the MessageBox function.
''' </summary>
Public Enum MessageBoxResult As UInteger
     Ok = 1
     Cancel
     Abort
     Retry
     Ignore
     Yes
     No
     Close
     Help
     TryAgain
     ContinueOn
     Timeout = 32000
End Enum

VB Definition:

public Enum MessageBoxResult
     Ok     As Long = &H1
     Cancel     As Long = &H2
     Abort      As Long = &H4
     Retry      As Long = &H8
     Ignore     As Long = &H10
     Yes    As Long = &H20
     No     As Long = &H40
     Close      As Long = &H80
     Help       As Long = &H100
     TryAgain   As Long = &H200
     ContinueOn As Long = &H400
     Timeout    As Long = &H7D00
End Enum

Notes:

None.

Managed API Alternative:

System.Windows.Forms.DialogResult