In most printed travel guides there is information about departure taxes you need to pay on departure from Tribhuvan (KTM) airport in Kathmandu.

But from year 2010 there is no such departure fee any more for international departures. All taxes are included in your ticket.

Thought you still need to pay domestic departure fee. As of April, 2013 this fee is 200 Rupees. So if you are flying from Kathmandu to Lukla or Pokhara be ready to have some spare cash to pay these taxes.