Helical double-pipe heat exchangers have been widely investigated because of their compact design, small volume, high heat-exchange area, and potential of generating secondary flows due to helical curvature effects. However, changes in the geometry of the heat exchanger, including helical pitch, might affect the flow structure, pressure distribution, and heat transfer simultaneously. In this study, a three-dimensional Computational Fluid Dynamics (CFD) analysis is performed to investigate the impact of helical pitch on hydrodynamic and heat transfer characteristics of a vertical double-pipe helical heat exchanger. The equations of continuity, momentum, and energy for Newtonian incompressible fluid are solved numerically using finite-volume-based approach implemented in ANSYS FLUENT software. The effect of three different helical pitches of 151, 191, and 231 mm is analyzed while all the other geometric and operational parameters are kept constant in order to focus on the effect of pitch modification. It is found that decrease in the helical pitch increases the heat transfer coefficient along the helical flow channel. The main cause for that is related to the higher number of turns in the same axial distance and the enhancement of the curvature-driven secondary flow, which facilitates fluid mixing and decreases the thermal boundary layer thickness. On the other hand, decrease in pitch affects the pressure distribution and leads to an increase in hydrodynamic resistance due to more intense secondary flow. Hence, although the smaller pitch is preferable in terms of heat transfer improvement, the selection of the pitch cannot be made only on this basis. It is necessary to conduct a combined thermo-hydraulic analysis of heat transfer improvement, pressure drop, and pump power demand in order to define the most appropriate pitch value.