The objective of this work is to investigate frictional pressure drop during adiabatic liquid-vapor flow inside minichannels. New experimental pressure drop data, relative to two-phase flow inside circular and noncircular horizontal channels with hydraulic diameters ranging from 0.96 mm to 2 mm, is presented. By analyzing this data the present authors updated the two-phase frictional pressure drop model presented by Cavallini et al. (2009) [16,17], developing a new equation to calculate the effects of surface roughness on the frictional pressure drop as a function of the liquid-only Reynolds number. The present updated model is validated against experimental data and compared with other available correlations. (C) 2013 Elsevier Ltd. All rights reserved.