In the last few decades pile foundations became one of the most important sources of resistance against lateral loads. The paper presents the study of single laterally loaded piles, embedded in non-homogeneous soil and subjected to cyclic loading, using the sensitivity analysis approach. The sensitivity of maximum lateral deflection due to the changes of the design variables is investigated in a theoretical fashion. The design variables considered are the properties of both the pile and soil. The sensitivity results are given in a graphical form that reveals how the changes in the design variables that are crucial for the performance of the system are distributed spatially along the pile axis. The paper investigates the effect of the pile head boundary condition on the sensitivity results. A comparative analysis between piles with different head constraints is presented. It is shown that the sensitivity results connected with the pile bending stiffness are the results mostly affected by the change in head condition.