Using the forward method on the IProjectedCoordinateSystem can be used to get the desired results.ISpatialReference pUPS = pSpRefFactory.CreateProjectedCoordinateSystem(32661); WKSPoint wksPnt = new WKSPoint();wksPnt.X = -132;wksPnt.Y = 90; Debug.WriteLine("Pre Conversion : " + wksPnt.X.ToString() + " , " + wksPnt.Y.ToString());((IProjectedCoordinateSystem)pUPS).Forward(1,ref wksPnt);Debug.WriteLine("Post Conversion : " + wksPnt.X.ToString() + " , " + wksPnt.Y.ToString());