Two-phase flow approaching singularities such as abrupt expansions and sudden contractions is widely encountered in typical industrial and heat exchanging devices. There have been some studies concerning this subject but they mostly are applicable for larger channels. In this study, the first attempt is made to review the existing efforts concerning two-phase flow across sudden expansions/contractions and to examine the applicability of the existing correlations with respect to the recent data in small channels. The second part of this study presents some newly measured pressure drops and observed flow patterns pertaining to some special flow phenomena by expansion/contraction. For an abrupt expansion, it is found that the existing correlations all fail to provide a reasonably predictive capability against the newly collected data. Furthermore, a unique flow pattern called "liquid jet-like flow pattern" occurs at a very low quality region of total mass flux of 100 kg.m(-2).s(-1), and it raises a setback phenomenon of pressure drop. By contrast, an appreciable increase of pressure difference is seen when the liquid jet-like flow pattern is completely gone. A similar conclusion is drawn for the data of contractions. For the correlations/predictive models, the homogeneous model gives satisfactory prediction for conventional macro-channels but fails to do so when the channels become smaller. This is especially pronounced for a small-diameter tube with a Bond number being less than 1, in which the effect of surface tension dominates.