Design of helical springs are well defined and studied thoroughly. Generally, behavior of stiffness is considered to be in linear regime with desired dimensions. However, as the spring index which is defined as ratio of helical diameter to wire diameter gets lower a correction to calculated stress values must be performed. Furthermore, collision between coils, non-homogenous pitch heights between coils, end conditions are other factors leading to increase in stress values as compared to intended design values. An unexpected premature crack formation in a fatigue tested helical compression spring was investigated. First, geometry was measured using CMM and compared with design tolerances. After, metallurgical inspections regarding composition, hardness and microstructure of the material were performed. An analytical and numerical study was conducted in order to evaluate the stress state in the spring. A finite element model was created using ABAQUS and stress increase due to end condition was observed. A premature failure in a helical spring was studied regarding dimensions, material and stress state. The factors leading to nonlinear response of the spring is addressed and compared with experimental tests.