Over last two decades, plate heat exchangers (PHEs) have presented themselves as a viable alternative to the conventional shell and tube heat exchangers in the process and power industries. The thermal theory available for plate heat exchangers in the literature largely works on the assumption of equal flow in each channel. However, it is well known that the distribution of fluid from port to channel in PHE is far from being uniform. The present study brings about this port to channel flow distribution effect on the thermal behavior of multipass plate heat exchangers. The variation of the heat transfer coefficient due to flow variation from channel to channel has also been taken into consideration. Heat exchangers with both equal and unequal passes of the fluids have been studied. The results indicate that the flow maldistribution severely affects the performance of plate heat exchangers, and multipassing can act as an important tool to reduce the deterioration in performance due to maldistribution. The results show that with a low number of passes, the increase of velocity of fluid may be counterproductive in terms of heat transfer enhancement. Also, adding plates in order to increase the heat transfer surface may not be effective due to an increase in flow maldistribution. The correlations for 1-1, 1-2, 2-2, and 2-3 pass plate heat exchangers with the maldistribution index as a parameter are also presented.