string directoryPath = "WinNT://somedomain/someuser";

string fullName;


DirectoryEntry directoryEntry = new DirectoryEntry(directoryPath);

if (directoryEntry.Properties["FullName"].Value != null)

{

fullName = directoryEntry.Properties["FullName"].Value.ToString();

}

One issue with this code is that when "somedomain" actually corresponds to the local machine name (because your are trying to retrieve the "FullName" of a local account), it can take an extremely long time to run. This is probably because the underlying framework is off trying to find a domain controller before falling back to the local security store.

To work around this, consider code that would look like the following when formulating the directory path:

string[] identities = windowsIdentity.Name.Split('\\');

string directoryPath;

if(Environment.UserDomainName.Equals(Environment.MachineName,StringComparison.OrdinalIgnoreCase))

{

// special case needed for "off domain" case.

directoryPath = "WinNT://localhost/" + identities[1];

}

else

{

directoryPath = "WinNT://" + identities[0] + "/" + identities[1];

}