Observations suggest that thin current sheets forming in the near-Earth magnetotail late in substorm growth phases may be a crucial part of substorm evolution. In a simple theoretical model the current density was shown to become singular for suitable external perturbations. Here, we address the same problem in a more realistic model based on the adiabatic MHD-theory developed by Schindler and Birn [1982>. We show that under suitable conditions the formation of a thin current sheet in the near-Earth tail is an intrinsic aspect of flux transfer to the magnetotail. The mechanism is based on the strong variation of flux tube volume with the magnetic flux function. ¿ American Geophysical Union 1995