A new model to calculate the two-phase pressure drop across a sudden contraction in a duct area was developed and checked against data recently obtained with mixtures of air and water, aqueous glycerol, watery calcium nitrate and with the freon 12. In addition, data available from the open literature are considered. In the model all relevant physical parameters are included and, in contrast to correlations published so far, the entrainment of liquid in the gas stream is taken into consideration. The predictions are validated for a wide range of conditions, pipe diameters and physical properties typically encountered in industrial piping systems. Calculations based on the new approach are sufficiently accurate for engineering purposes.